alphasonik is crap.
You will get better response and overall performance with 2 10" subs under the seats, the JL 10w3 v2 work VERY well for moderate power levels.
IF you do have to have 12's, be prepared for extremely peaky performance, and very sharp low frequency rolloff. In other words, it'll sound like crap.
BP is right, Diamond is good stuff, but most of the subs they use are more oriented towards vented enclosures.