When I started digging through that thread I thought, he could have bought an old ass van or something and done the same thing without ruining a nice car. Then again thats what he wanted and was going for, still good looking work.
My current system consisting of 2 Image Dynamic Id's, Kole Audio Q-1920 amp, and each driver having a ported 2.0 cu. ft. enclosure is a real pounder. Only paying $200 for the subs and amp, and about another $75 in box making material and wiring, and lasting well over years now, I'm going to stick with the same brand and upgrade the amp.
Turns out I won't be saving much room however, the driver is about 1 cu. ft. alone and needs 2 cu. ft. to go with it. So my box is looking closer to 3-3.25 cu. ft. down from 4. Saving a little bit of space anyway. Gaining a little space, a much more efficient amp, and a driver that will be able to hit lower and harder. Might not be as loud since I'm dropping down to one but it will sound so much better.