You probably don't want to do this. I tried this on a whim in my car, and the results were miserable. It vibrated EVERYTHING in the car. It sounded awful. If you want to go this route, you will need to make a fiberglass tub in the spare-tire well, and heavily sound-deaden the well. My roommate and I took the tire bracket out of his tire well and are currently constructing a fiberglass enclosure for 2 15's. It's not hard at all, just a little time-consuming. It takes quite a few layers of fiberglass to make it rigid enough, and a lot of bracing. It's possible to do a fiberglass enclosure in the well without removing the bracket, but you might have to bring your baffle up a big so the magnet(s) clear that bracket. Let me know if you want to go this route and don't know how to work with fiberglass.
Clint
>i got a board i'm cutting >and gonna cover with vinyl >for use as a floor >board for my trunk. the >question is does anyone know >of a good 15" woofer >that is possibley "freeair" or >what if i installed a >gasket on the back of >the wood and bolted it >down to the chassis and >use the spare tirewell as >a box? or should i >just get a 12" woofer >and buy a small box >to mount to the underside >of the board?