Looks nice! I think it might fit in second gen Blazers too, because the interior of the car pictured looks exactly like the inside of my '96 blazer. GLWS
Using a rubber surround will lower the FS by adding more mass, which also increases MMS (moving mass) and could change the CMS (Suspension compliance) depending upon how stiff the foam was compared to the new rubber surround.
Yes. I know someone on fiberglassforums did it with a pair of JL 8's. I think he said his box was 1/2 inch thick? I looked for a good 20 minutes and couldn't find the exact thread though... It would be freaking expensive though. You'd probably be better off making a fiberglass box and...