[anthony]

I've been thinking of doing the same thing with a custom console. It appears that you can fit a single 8" sub in there.

I saw that JL Audio makes a 6.5" subwoofer (model 6W0-4). I was thinking that two of those wired in parallel might be good too. They require a .175 cu foot sealed enclosure. The only thing I don't like about them is that they aren't very efficient (only 82db). Kenwood has a 6.75" sub that has a 90db efficiency.

Another thought was making a custom enclosure that fits under the dash. There seems to be a lot of room under there especially on the passenger side and it wouldn't take up leg room.