I too got tired of the "where to put the subwoofer dilemma."
This past weekend I purchased a MTX Thunder T8104A 10 in. subwoofer. It's sitting right behind the driver's seat in a sub box with the the speaker pointing right at my butt.
It's being powered by a MTX Thunder 6152 amp; bridged, it's running a little over 300 watts.
I put about 7 feet of speaker wire on it, so when I want to fold down the midgate, I just move the speaker off the floor, fold the midgate down and the put the subwoofer on top. There's even enough room to move it to the front seat if need be.
I looked at all the solutions on this board and just didn't think I'd be happy with anything smaller that a full size 10 in. sub.
I might have been happy with 4 12's mounted on my midgate, but that might be a little overkill.
Good luck,
DrJ