my only problem is the car is a 2001 jaguar s type.. now do you think the 13.5 at 1.875 cu ft would fit back there.. because a freind of mine has the same car except his is a 4.0.. but same trunk space, anyway he has 3 8" Digital Designs and it sounds good...
Ben, if your looking to save space and want a sub that will sound amazing and still get very loud sealed look into the Hertz Mille 380. You can only buy them from Hertz dealers and they go for ~$800-900 which is pretty expensive for a single 15" sub. However you can run them in a 1.5cuft sealed box and they sound absolutely amazing.
Heres a review from car audio mag. http://www.caraudiomag.com/features/caep_0712_hertz_mille_ml3000/index.html