A sub mounted in the rear door is awesome. I have a rockford fosgate 12" stage 3 shallow mount in a sealed enclosure. Amp is mounted under the drivers seat so there is no real loss of storage space and with a metal cage over it I dont have to worry about cargo shifting and damaging it. And it will BOOM.. Think I got the sub on amazon for 99 bucks a while back, and built the enclosure myself and covered it in vinyl to give a clean look