I'll bite - Did a stealthbox over this past weekend.. Total time invested was maybe 3.5 - 4 hours..
So fiberglass the easy way..
First I shot the spare tire down with release agent just in case I had a leak.
Made a quickie cardboard platform for the bottom.
Made a "Ring" out of 3/4" MDF. Set the height so that the top of the box would be about 1/4" below the cargo lid.
Then attached edges of dropcloth to hatch seal and used dropcloth to line the spare tire. Sprayed with release agent.
The the glass - 2-3 layers of cloth for the form.
After 4 hours I popped it out (still a tad soft) so that I could add 2 layers of 1.5oz mat without having to sand ..
You can see the impression of the dropcloth.. If you REALLY care you can sand it smooth.. I don't.. - This is a stealthbox - not a showpiece..
Found a spot that some terminals wouldn't interfere on the underside of the box.. Using
plugs for quick access to spare.
This is probably the thickest the glass gets (thicker on the flat surfaces).
But I generally follow the "rule of thumb". (If you press on it with your thumb and cant make it move - good'nuf)
I didn't take pictures - but I attached a ring to the underside of the top of the box to mount the sub with about 1" of room for excursion.. Mounting depth is still just a shade over 6" available.
Finished the top off and covered it in black felt.. (Easy to work and I don't need durability).