To answer your sub question, if you do go forward with the subs, the boston ovals take a lot of power and would be much shorter than a normal 12 but,
you could always do the rear center console idea. i did one with 2 sa 8's in a ford crew cab and it got pretty loud off 800 watts on each. if you go up onto the seat im sure youd have enough room for the 12's plus have room under the seats for the amps and battery. i always worry about mounting em forward under the seat since theyre super liable to get kicked. Just my opinion. Your builds always end up nice so im sure you'll figure it out.