I actually mail ordered all the stuff to make the sub box. A friend of mine that is pretty knowledgable about composites recommended Aircraft Spruce as a source.

I used Rutan bi-directional weave glass and West System epoxy (much better to work with than that Polyester stuff, which is pretty messy and toxic, plus it shrinks over time). I have built many fiberglass enclosures in the past, but this was the first non-polyester resin based one.....

Some links to the appropriate catalog pages are below. They have better stuff that could yeild higher strength to weight ratios, but I felt this was the best bang-for-the-buck. I wanted a box that would be strong but add minimal weight to my car....

http://www.aircraftspruce.com/