Well, do you want to go sealed, or do you want to go IB? IB bass is some of the best I've heard, but you need to build the baffle right, a rectangular box is usually much easier to build. For IB, you really should build a baffle behind the rear seats, and rear deck, regardless of where you mount the sub(S). If you're willing to pull the rear seats out to build a baffle, and rip up the rear deck for the second baffle, you can get very impressive results. If you want to keep it simple, use a sealed box.