Very similar to what I was going to do.
I've got an 05 SuperCrew, I think we've talked before
I'm doing the same thing you are, except I'm doing an RD Heavyweight 15 in a 4th order //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
Seat riser kit+ two nice 12's = pretty **** loud in that truck, and still able to sit in the back semi-comfy
Kenny(he's on the forums as jack something) has an F-150 with two single spider RD Alpha 12's on an RD 1750.1 and is doing a 45.xx legal on the dash with them. Sealed, under rear seat.
Good luck. I wont be doing my build(but I'll still get pictures so I can post a semi-log) and I cant afford new components yet so stockers will have to suffice for a while //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif
Look forward to seeing it bossman.