I can confirm that it does little good to put a sub in that little compartment... I put a 6.5 inch Rockford Fosgate woofer in there, replaced the amp in the trunk with a bigger Alpine, the head unit with a newer Alpine, and put Boston Accoustic pros in the doors. More than a grand later, it still sounds tinny when the engine's running and has no real bass.
Sounds pretty darn good when it's parked now, lol.