We just got done installing a 18" RD Audio Custom Built sub into a 2003 Escalade.
The Sub is an RD SPL based motor,with some softpart swaps done. The box is 6.5 cf@ 32 hz. The amp is an Atomic A2200.1. The sub is seeing roughly 1800 rms. It gets LOUD and LOW!!! Plays any kind of music from Rap to Country beautifully.
To give an idea, it was raining that day, and the front windshield whipers couldnt wipe the rain off when the bass hit. It knocked the blades off the windshield and you could see the patches where it missed, LOL