As we all know, the OEM sub doesn't hit very hard. After trying to sell my old radio out of my old car unsuccessfully, I decided to use the amp and subwoofer for the Ram. So, I ordered a PAC SOEM-T LOC ($15) and an Atrend BBox 12" enclosure ($60). Here are the results. Sounds great and pounds just as good as my old 14"x14" enclosure.
PowerZone Crunch PZA700.2 amp fits perfectly on the floor behind the 40% cushion. Don't even have to lag it down. The cushion snugs right up against it.
PAC SOEM-T line out converter. Still need to trim some speaker wire.
Rockford Fosgate R2D2 12" and Atrend BBox enclosure. Had to rotate the sub as you see it since that was the only way it would sit flush. The 12" is tight and a sub with a larger footprint will not fit.
Grills leave marks on the underside of the cushion. No biggy.