FYI - if you aren't just trying to go for the loudest you can fit... and are considering quality... do not overlook 8" or 10" subs in a properly designed 3rd order (std ported) box.

You can get very nice low end, keep it in a realtively small enclosure, and by placing it in the rear of the vehicle, and optimizing further by aiming the port towards the front of the truck, you might be amazed at how much low end (deep bass around 40Hz) you hear in the front seats... Power requirements should be a bit less than larger subs as well (assuming you cut off the lower frequencies the box can't play (30Hz below))

-=RB

-=RB