The best system for a standard cab, is to use subs in the doors and mid ranges and highs in the dash, all ran through an amp and x-over. Now you aren't going to get the teeth jarring base out of the door subs, but you will get decent all around sound, without having a sub pointed at your back, and driving with your nknees by your ears <img src="/forums/images/graemlins/lol.gif" alt="" />. Besides, any type of sub in a box in the 7" of space behind the seat wont sound much better given the limited amount of room the box will have. If you have to have the big base sound effects, install a shell, or 1/4 shell and put the big 12-18" subs back there.