[Deuce-Koup]

You could always have a fiberglass box made to fit just behind your wheel well in the trunk. That would give you great sound qualities, slick look, and leave you with most of your trunk space intact. Anywhere that does custom audio should be able to work something out for you!

 

[Deuce-Koup]

Yeah... There really isn't a whole lot of space under the rear seat.
Although, the Nissan GT-R has a center console instead of a middle seat in the back and there are a couple speakers mounted in there. I bet you could do something to that affect if you wanted too.