I blew my 3215 in 2 weeks with a Hifonics Colossus on it and the gain was halfway turned up. Goliaths = poo no joke. My one 15 got LOUD but didnt last and the cooling was a POS. Get a Maxximus sub.
I had a hard time finding my 3215 and you will probly have a much harder time finding more because they have a brand new line. I would really recommend (1) Maxximus sub. That thing took 6000 RMS like nothing when I saw it!