Need Help on Sub Idea!!!

[Disinger 0]

I have a 94 camaro and I am currently running an old school Memphis 500 D amp to a single P3 in a 2.3 cubic ft sealed box. Obviously space is my limit. I am looking to get my hands on one of the MD2D US Amps. I cant decide if I wanna add another P3 and run two 12" or upgrade my sub to one kick ass 12. If I do so I would like to keep the same box I have. I am after some deep bass, something that can take your breath away.

Also, what is your thought on a ported or slot vent box in a camaro? I have heard both good and bad.

Any ideas or suggestions would be greatly appreciated. Thanks!