Its just so darned tight in the passenger area. Do a search for under the seat subs, or low profile amplified sub and you might find something that would fit down low behind the seat. I already owned a Infinity Bass link which I used in my suv. When I got the crossfire I mounted it in the back off to one side as far as possible. I'd have a little more trunk space if I mounted it upright, but I found the it performed better mounted flat on a board. It works very well.

Tom