Got it done. Read along.
This is not an all inclusive tutorial as there are several reference sites devoted to this project. I read those prior to doing my project. This is just one way and the way I did it.
Resin (at least a gallon)
Liquid hardener (buy more than provided with resin)
Cheap measuring cups
Cheap paint brushes
Spray adhesive (3M Super 77)
Fleece (cheaper is better and about a yard depending on overall dimensions)
After you have an idea of what you want and where you want it break out the masking tape. The area you tape off needs to be about 4" larger than what you think your finished project will be. In my case I knew what I needed for airspace in my subwoofer enclosure so I took some rough measurements to figure this volume out.
DO NOT SPARE THE TAPE!
Once the area is taped off with 1 layer go back over with another layer the opposite way. It should look something like this when your done.
For the first layer of glass I used fiberglass mat (not cloth) because you can form it to the unique curves better without wrinkles and air bubbles. REMEMBER fiberglass resin does not make fiberglass strong, the fiberglass creates the strength.
Take your fiberglass mat and tear it by hand into pieces about the size of your hand. Tear up a lot of it. The reason for tearing is that it forms better than the compressed form it is packaged in. Now is the time to cover anything that may possibly inadvertently come in contact with the resin. Resin does not come off of fabric or many other surfaces once cured.
Mix the resin and hardener. This is best accomplished by following the manufactures recommendations. I used about 8 ounces of resin for the first coat mixed in two 4 ounces batches. Once this is done time is ticking. Paint a thin layer of resin onto the tape, this will act as a tack coat to hold your torn mat. Take a piece of mat press it onto the resin then take a small amount of resin on the brush and dab it in a stabbing motion on the piece of mat your laid down. The fiberglass mat will soak the resin up but it may take a second. When sufficient resin is added the fiberglass with appear almost clear. Continue this process of adding mat and resin till the area you want to cover is covered with some mat overlap from piece to piece. It will look like this when the first layer is done.
Now let this layer cure about 2 hours. If you want you can do a second layer before it completely cures. I took a gamble that 1 layer would be enough to remove from the car to continue the glassing process, and I lucked out. This is what I had when I CAREFULLY removed it from the car after it cured at least 2 hours.
Once removed from the car you will begin adding more layers of fiberglass, this time fiberglass cloth. I precut and test fit some of the cloth for the compound curve areas to make my life easier when applying it. The cloth will cover larger areas and is rumored to be stronger. I added 5 layers on top of my initial in car layer. This took me a few days to complete due to my schedule and availability on this project. If you have time you could get it done in as little as a day I'm sure. The process for these layers is the same as the initial layer. My advice here is to work in sections using 4 to 6 ounces of resin at most. I found that anymore than this and your resin starts to cure. You will need to change brushes through this process as they will begin to harden. I was able to get through 2 batches of resin before grabbing a new brush.
When you have the number of layers you desire and the resin cures, about 2 hours, you can trim the ragged edges. This is the result.
Place this back in the car and check for obstructions such as trunk weatherstrip area and the trunk hinge. Once you are satisfied that all is well you need to add the dowel supports you see in the previous photo. These supports will support the subwoofer ring and are held in place with hot glue.
The subwoofer ring is made from 2 layers of 3/4" MDF if you want your sub recessed. A single layer is fine if you want a surface mount. You are going to make your ring to the dimension advised by the manufacturer. They will tell you overall size, basket size, required mounting depth and airspace. I have a router and table that makes this step much easier.
Now you will get to see some progress. I stapled the fleece around the inside of the subwoofer ring and then sprayed adhesive over the edges of the fiberglass mold. Stretch the fleece over the mold and onto the adhesive. Make sure the fleece is tight and free of wrinkles all around. It will look like this.
Once you have it done put it back in the car and check clearances again.
If everything looks good, then let glued on fleece dry for a couple hours.
Mix up some more resin. Thus time THOROUGHLY coat the fleece. More is better here. Once saturated let it cure for a few hours. You will end up with this.
More fiberglass cloth over the fleece. Once again I did 5 layers over the fleece for strength. Make sure you overlap your pieces for strength. Remember flat areas are prone to being less ridged than curves, just like sheetmetal. After this is done you can cut the subwoofer hole out and reinforce the inside corners and anything else you think needs strengthening with fiberglass mat if you wish, remember to tear this stuff.
This is your finishing stage. If you plan to paint then get out some fiberglass reinforced bondo and a lot of sandpaper. Vinyl does not require as smooth a surface, but is rumored to be a pain to do. I chose carpet. Not a lot of sanding and it can be had in a multitude of colors from a hobby or fabric store. Try and get carpet with no backing. Household carpet is this type and will not stretch to the curves like unbacked.
Wire it up and enjoy. I drilled a hole in an unseen portion of the box, ran my wire and sealed with epoxy.
And there you have it.
Questions?, comments, concerns, let me know.
I am working on the amp rack now and I'll post some pics when that is done.