On the topic of car bass, I agree with Eargasm, the combo of cabin gain and Epi with 600w on tap calls for a sealed 12 or 15 in my books. I am running isobaric 10's in my Accord, as I was not willing to give up much trunk space. Chops, I have an older Fosgate 12 inch (cast basket, 500w rms, 1000w peak) in my basement, dormant... check your PM. I used it in a 1.25 cubic foot sealed box in my BMW, run off a 500w Memphis Audio Class D amp - great tight car bass, and hit the lows. With the Epi, it would work very nicely.
Back on topic, I would go with 1 12 for a room of that size.