why do you need to keep the amp on the seatback as well? there's tons of places to stash amps in this car...
i did seriously look into building subwoofers into the seat back. enough that i bought a replacement seatback, and 2 of
these subwoofers.
the airspace requirements of 2 of them are approximately that of the trunk space.
i gave up when i figured out that the seatback is about 1.5" thick, and the subwoofers were 3.5". i wanted the design to maintain all available trunk space, but also to maintain the flat loading surface of the seatback. when i figured out that was unattainable, i bought a image dynamics fiberglass box instead.