Fiberglass info

I am new to fiberglass, but have recently been reading up on a few threads and it doesn't look all that hard.  I do have a few questions though:

I have read a few columns where people use shirts, fleece blankets, and other things to stretch over the enclosure.  Whats the best?  One column in specific used a "Rage Gold fiberglass fleece" and then placed the resin over it.  Is that a good brand, Rage Gold, and where can I get some?  Do you lay the resin over the Rage Gold Fleece and then lay the fiberglass over it?

Primer.  I have read that some people use a poly-primer that goes on thick, and allows for sanding.  Where can I get my hands on some of this?

The last question is about structural integrity.  I am building the box for my 2001 Jeep Grand Cherokee Limited.  I want it to conform with the wheel wells and the back of the seat, and then angle each of my subs towards each other (Memphis HPO 12's.)  Should I build the entire box out of fiberglass, or should I build a base out of MDF?  Will the box be to fragile to build it completely out of fiberglass? 

Thanks for the help.