DIY Fiberglass Stereo Enclosure
Originally Written Oct. 18, 2010
by Shane Martin
The Wholie Shop

This article will take you from start to finish through the design of a custom fiberglass enclosure. The ATV we will be building this for is a 2003 Honda foreman, the enclosure will feature a stealth intake snorkel, (2) 6x9 speakers, a mechanismless head unit and a GPS.

A good way to start is to cut out a base template using cardboard to fit the front rack, you don't want to make it too large or clearances too tight as it is going to grow about 1/4" all the way around by the time you're done.
Once you're satisfied with the base shape use the template to transfer the shape to some 1/2" plywood. Marine plywood will last the longest.

*note* the photo shown here is the rack of an arctic cat... The original picture from 2010 is missing.


Next clamp the base down to the rack to keep it from moving around, for this build we needed somewhere to mount a GPS, the Control Unit and a couple speakers. A Flat center panel was cut, along with some wooden speaker rings. Use a high quality construction adhesive to secure the wooden panels and speaker rings in place. Pick something that looks pleasing to you from the drivers seat.
The screws shown in this picture were trim screws just tight enough to hold the wooden rings & panel until the construction adhesive set, then they can be removed.

It helps to go ahead and pick out what features/components your enclosure is going to have before starting a project like this. That way you can make sure everything fits!
For this enclosure we selected a Clarion CMS1 which will do AM/FM Ipod & USB all in one unit, it's also got a built in four channel amplifier which will drive a set of 6x9's or 6 1/2" speakers quite well..

We also decided to incorporate this pelican box as watertight storage, we will punch a hole in the bottom, run our wires into it then seal the hole back up to keep it water tight.
Our enclosure will have a nice dry storage spot for our cell phone/camera/ipod etc.
We ended up cutting the tabs off the box on the sides to make it fit flush in the enclosure.

A stealth intake snorkel was also added to this enclosure, to do this we disconnected the factory air intake from the air box then piped it up under the front fender. Once we had decided where to bring the pipe up through the fender we cut a hole in our plywood base and attached a fitting that would allow us to remove the enclosure if needed.

The idea here was to completely seal off the snorkel from the internals of the box, being as this is going to be a reasonably large enclosure if it were to fill up with water it would be extremely heavy!
Thus the basic shape of a tray was formed out of cardboard, and the excess snorkel pipe trimmed flush. Once the fiberglass cures we can just open the hole back up.

Whenever you build rough shapes out of cardboard, some hobby felt will go a long way to giving your finished project a uniform shape. Lay in some felt and as you start to glass the felt will help to conform the glass to the basic shape but leave it much smoother than just trying to apply fiberglass directly to the cardboard.
Next cut a couple pieces of fiberglass mat, make sure there a bit larger than the actual finished product! Next mix up some resin per the instructions; paint it on the felt, then lay a layer of glass then again coat it with resin. Here we ended up laying 2 layers of fiberglass.

Once the resin is cured you can trim off the excess fiberglass, the previous photo you can see we didn't paint the overhanging edges of the mat with resin, as we were just going to have to come back and cut it away. Fiberglass mat without resin will trim easily with scissors.
Once you've rough trimmed it it helps to have a rotary tool such as a rotozip or dremel with a tile bit. Cured fiberglass is quite hard to cut otherwise.

Next the hole for the snorkel needs to be opened back up, as this chamber will soon be closed and we will have no way of getting back inside it! Again a roto-zip with a tile bit will cut through fiberglass effortlessly.

Once we were satisfied with the basic shape of the tray. The cardboard form can be ripped out and discarded, the fiberglass tray can be glued in using PL Construction adhesive and some recessed screws.
To make an attractive opening for the snorkel intake we used a metal backing strap and bent it into an arch, this will form the opening leading into the snorkel chamber, it was glued in place and bent to what we thought would be a good contour for the fiberglass to follow.

Now the enclosure can finally start taking shape!! Lightweight hobby felt can be purchased from a hobby supply store such as Hobby Lobby. This particular enclosure ended up requiring about 2 yards of felt to complete the project.

Staring on the bottom of your enclosure, secure the felt with staples and then using spray adhesive stick it to the flat areas such as the front plate and speaker rings. This felt is going to define the final shape that the fiberglass will follow as you lay down the glass.
Stretch it good and tight over the enclosure and avoid bunching the felt up in the corners if possible.

Here you can see the outline of the speaker ring and where we've trimmed out for the GPS unit.. You can also see where the metal strap has formed a nice arch, this will be cut out later for our snorkel intake.
Note: If you have fabric bunched up on the INSIDE of the box it will be okay for now, it can be trimmed later using a sharp razor blade but for now leave it there.

Heres the enclosure sitting on the rack wrapped in felt. We ended up adding another flat wood panel on the top to box in the waterproof storage box..
Now would be a good time to test fit all of your components! You want to ensure they will fit in the openings you have. Everything should be nice and snug at this point with the felt glued into the openings.

The idea behind the felt is to give the box a contoured and rounded look, as you can see on the front where the felt is stretched down to the base it's nice and curvy. Remember the shape you have here is pretty much the shape its going to be.. Remember! The tighter and smoother you can make the felt the less sanding and filling work you'll have in the end.

Again remember to test fit everything, once you start laying fiberglass you're commited! Here the speakers, waterproof box, and GPS unit are shown.. The only part that isn't pictured is the control unit for our clarion CMS1. It will be installed to the right of the GPS and below the waterproof storage box.

okay now time to get messy.... Lay down some card board on the floor and block up the project so you can get your hands under it. You'll need to coat the exterior fabric with resin and let it set up so the enclosure will hold its shape.. Once this dries we can start laying fiberglass.

We recommend using the chopped fiberglass mat that is made up of many small fibers rather than the smooth woven mat. We've found that for forming around tight spots or creating complex shapes the chopped mat works infinitely better!
Start by cutting all the fiberglass that you'll need and lay it nearby so that you can get to it without running across the shop. At this point you should probably recruit a helper to mix up small cups of resin/hardner. You don't have a lot of time to work and smooth the glass before the resin starts to set up. This project required 1 1/2 gallons of resin and 3 1/2 packs of fiberglass mat (8 sq feet per pack)

Here the first layer of glass has been laid, You want to avoid any white spots (the white spots here are going to be cut out anyways but avoid them on the actual enclosure)..

1) recruit a helper to mix up resin & hardener for you so you can keep working.
2) Get some disposable rubber gloves and a couple buckets that you can get your hands in.
3) scoop the liquid resin out and smear it on the felt layer, then grab your first piece of glass.
4) lay down your first layer then completely saturate it in resin by scooping the resin out and smearing it in with your hand. It takes a lot of resin so have your helper measure out the next bucket full and add the hardner just before you run out.
5) continue laying the glass being sure to completely saturate it then work it around your corners and contours.. The hardest part will be getting the glass to fold under the box and stick to the bottom!!




Continue laying glass until you have three or four layers down, then using a roller you should squeeze out any excess fiberglass resin and continue to work your glass around the corners and under the bottom.. It took about 20 minutes to lay these three layers and get them worked in.. Let it cure then you can cut out the openings again.

Now that the fiberglass has cured it should be very rigid and hard, we used a roto zip to cut the glass out of the openings, be sure not to cut any deeper than until you see the felt disappear and the wood showing below, this ensures you won't make your new opening too large! Cut a bit at a time trimming it back then test fit your components again.

Here you can see the thickness of the fiberglass, 3 layers = 3/16" inch, 4 layers = 1/4".. Its VERY strong at three layers, there really isn't much point to make it thicker.

Once all your openings are cut out and you've test fitted your components again the entire project needs to be sanded with 40 grit sandpaper on an orbital sander. Knock off any stray fibers and generally smooth it up.. The surface needs to be completely sanded so the body filler will adhere properly.

This stuff is available at local auto body supply stores, it's thinner for auto body filler. You need to mix it about 5 parts filler 1 part thinner to thin out the body filler. You want it thin enough to paint on with a brush as it will go on much easier.. If you can't find this stuff you can also thin the body filler out with fiberglass resin. Mix up the filler & resin or honey then add the required hardners per the filler instructions (and resin if used instead of honey)

Paint the filler on with a brush, it helps to have a helper mix this stuff too because you only have about 10-15 minutes to paint the filler on before it starts setting up.. If you mix too much you'll never get it spread in time and you'll end up throwing part of a batch away.. You can work in small batches if you have a helper. Luckily even if it sets up before you finish it can be sanded right away and you can continue working.

Once it starts setting sand it with 30-40 grit sandpaper to find your low spots. You'll see the low spots right away, rough up the low spots then blow/wipe the sanding dust off and fill some more in. The better job you do here the better your finished product will look! The slicker finish you want the finer sanding you'll need to do. Start with 30/40 grit on a random orbit sander, sand the filler smooth and look for low spots.

Continue applying filler to the low spots, then sanding until you get a nice uniform coating of body filler over the entire enclosure, then start stepping up your grit, to 60 grit, then 80 grit. You can go on up to 800+ grit if you want a very smooth slick paintjob. Here we stopped around 100 grit because the end product is going to be sprayed with rhino liner.

Once you've got the entire enclosure sanded smooth, you can wipe the whole thing down with some denatured achohol. This will get any oils or contaminates out that might prevent the paint from adhering. Wipe it down then apply a etching primer to the enclosure before you start painting.

Once the primer is dry you can start applying your finish. Rhinoliner is quite tough, seeing as this is a trail bike a fancy slick finish would just end up getting scractched up. The enclosure as it sits currently weighs about 10 lbs with no electronics in it.

Once your finish cures you can go ahead and install it and hook up your electronics. For this project we installed the CMS1 unit first, wired up power and ground to our GPS, and set up the speaker connections. A hole was also drilled to run power wires direct to the battery, equipped with an inline fuse at the battery this enclosure will be able to be used regardless of if the engine is running or not.

We used a couple of 1" U bolts through the bottom of the base plate to secure it to the rack. Going through the bottom means that to remove the enclosure you would have to remove the left and right speakers. Once secured be sure to seal around everything with some silicone. We've found that black RTV silicone works well and will blend in with the rhino liner.
Here everything is installed, we've also cut out the hole for the snorkel chamber.



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