This section was contributed by Big Mack who frequents the SoundIllusions.net discussion forum.

What you would basically want to do is take out anything that you don't want to get resin on. The carpet comes out easily enough, and you WILL NOT get the resin out of it if you spill it or cut through plastic or anything. I highly recommend that you take out the carpeting.

First off, SAFETY FIRST!!!! A clean, well ventilated, and spark free (no smoking) work area are vital to this. You will need good rubber gloves, a couple of mixing bowls (not wax coated), several brushes that you can throw away, some grille cloth or fleece materials, a dust mask (not a necessity if the area is well ventilated, but I recommend it just the same), some body filler, and the resin materials.

After you have the carpeting out of the trunk (as well as whatever else is in there). Clean the area that you're fiberglassing. Get the vacuum out and really get everything out of there. It will make the job easier (and look much nicer).

Now that it's clean, lay down some plastic sheeting (plastic drop cloths work good and they're cheap). Tape it up so that the odors are restricted to the trunk area (that's a little trick Fishman taught me for doing tubs in spare tire wells to keep the car from stinking for days). You can even block off the rear speaker openings if they are in the rear deck for maximum odor protection.

Once you've got this area masked and protected, you can start the process. Beware that this takes some serious time, and you have to concentrate to do it right. If you're rushing it, it will either not come out right, or it will look like garbage (and sound similar). Lay pieces of grille cloth (I prefer this for starters because it bends easily and will dry fairly quickly in air or with a heat gun) around the area that you're 'glassing. Cut it in strips that overlap and don't have too many wrinkles. Once these are laid down, you can put on your gloves and mask and mix up a small batch of resin. Follow the directions on the container for mixing the resin with the hardener (too much of this, and it will dry with the brush in it and then you're done with that mix and brush).

Once you've got that mix ready, start to spread it out with the brush. Coat the pieces well, but don't put too much on or it won't dry for a long time. They should be soaked all the way through, but not dripping. Sometimes, you can just put the strips in the resin and lay them out, but this is very tricky to do without oversaturating them, so you must be extra careful when doing this.

Once you've got the entire area covered, let it sit for at least an hour. If you have a heat gun, you can go over it LIGHTLY with that to speed the process, but don't overheat it or you'll be looking at scorched pieces and plastic.

Once the first layer is fairly dry (doesn't need to be totally, just close), start the next layer, making sure to interlace the grille cloth like you lay bricks so that there are no seams that line up. Coat this one a little thicker (very little extra) than the first layer to bond the pieces together and make them stronger.

Let this setup dry COMPLETELY. Once this is dry (will take anywhere from 2 to 6 hours without heating, but can get down to under 1 if you're careful), you can take it out of the car if you want to not work in such a constricted area, provided that it's strong enough to hold it's shape (2 layers usually are, but it depends on how large it is).

You will want to get this piece built up to 1/4-3/8 inch. After you have 3 or 4 layers of grille cloth in it, you will want to put a layer of fleece in. It will take more time to dry, but will add thickness and more strength than the grille cloth along due to the tighter weave of the fleece. Again, exercise common sense and caution and work safely. I cannot stress this enough. If you start to get dizzy or light headed, put your work down, and get some air. Open the windows of your work area and let the fumes out. Please, be careful...

Now then, once you have your piece built up, you will need to make the top. This should be made of at least 3/4 material (preferably MDF or marine particle board). You cannot make a piece from fiberglass straight enough or strong enough to merit the time it would take to try, so just cut the MDF (using your workpiece as a template). Take grille cloth and staple it around the workpiece. Make sure that this will overlap onto the MDF by at least a inch (preferably 2). Shoot a couple of screws into the edge of the MDF and the fiberglass piece you made to keep it in place. Staple it to the MDF. You won't want to cut the hole for your speaker just yet, as it will make the job more difficult than it has to be.

Continue to build up the edges around and over the MDF until it is strong enough to hold the speaker sitting on it. It will not need to be as thick as piece you made since it is screwed to it and the MDF is 3/4 thick. You're basically looking for 2 or 3 layers of grille cloth on there to ensure a good seal.

If you want the enclosure to look really trick, before you 'glass the MDF in, you can take hardboard as thick as your sub's front gasket and cut out the speaker's entire outline (including mounting area). It will allow you to flush mount the sub into the tub. Once this is cut, screw it to the MDF and fiberglass the whole thing together as described above. Once you have this all screwed together and dry, you will want to test fit the enclosure before cutting any holes for subs.

Take the plastic out of the car since it won't be there when it's actually installed. If it fits like you want, then move on. If not, then determine why it's not fitting like you want and fix that area.

Since you're happy with the fit now, look at the bottom. If you want to smooth it out by sanding it and filling it so that you can paint it, now is the time. If you don't want to paint it, then you don't need to fill the bottom, but you should fill the top to allow for the carpet or vinyl to be smooth. Put a good layer of body filler over the areas that aren't smooth to the touch and let it dry (it dries fairly quickly, so this shouldn't be too bad). Once the filler is dry, you will need to block sand it so that it is straight and smooth. The block will keep you from grooving the 'glass (but you must be careful to not groove the entire block into it by pressing too hard).

Once you're satisfied with the smoothness, cut your speaker hole and cover the enclosure as you like. I like to paint the bottom even if the top is covered with vinyl or cloth just because I figure people show them off. Takes a few extra minutes, but it's only 2 or 3 coats of paint, sooooo.....

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NOTE:

The previous article suggests using a heat gun. If there isn't a significant amount of cross ventillation, there may be a fire hazard. Make sure that you read, understand and follow all warnings on the fiberglass resin container.

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The following calculator will help you estimate the internal volume of the wheel well enclosure. This drawing should help you understand how the volume is determined. Please keep in mind that the actual volume will be slightly different because the fiberglass material will take up some air space. This is only a rough guestimate of the total volume.