Want to make a Custom box, need help!

[thewifesyaris]

So I have had my rear seat removed from my car for over a year long now and have had a small bazooka tube in the rear. No with all of this extra room and summer around the corner I want to make a custom box for a 10" sub and tidy up the rear to make using that space a bit easier. So my plans are to place the sub and amp in the lower part of the cavity, where your feet would be, and raise that area up to the level of where the lower part of the seat would have been. In other words the trunk area will be level with where the seat would have been all the way to the front seats, with margin to allow the front seats to recline.

My question to those who have done similar boxs is what materials did you use to make the fiberglass box? I plan to use plywood for most of it, but I have only read up on a few here who have used fiberglass and resin to make a custom box. Any ideas of where to get something like that?