Ok, I've got a simple ported box design you could try for the Fi Q. Now keep in mind there are many other subs that would work in you application, but the Fi Q is good. This design uses all your space. The internal space with be about ~2 cubic feet tuned to 30-31 hz, with 29.25 square inches of port. The only issue with a sub like this is that it likes low tuning, and that generally means a longer port, which means more room taken up by the port, but it'll work.