The amount of room you have to work with will be one of the big deciding factors in what you run. Then your budget will come into play...Remember that to run a lot of power, you will need the electrical to back it.
Depending on the room available, you could run two good 15"s in a 4th order, ported through the rear deck...Budget will determine what subs and amps, but a setup like I described would be what I would do. If I were staying in the trunk at least lol.