Changing enclosure volume for SPL?

Sony's recommendation looks like (on WinISD) it creates a huge spike in the 40 - 50 Hz range.  The port is too small, but that is commonly seen in recommendations from the maker because longer/larger ports aren't easy to come by off the shelf.  The volume is a little small, too.  A good workable enclosure for each sub looks like:  2.0 ft^3....3 X 12 port  (tuned at 26 Hz).  But keep in mind some individuals like the results of bass boost, too....which is akin to the huge spike Sony has provided in the specs!  He might get the impression of louder sound if you just use Sony's data with the spike.  What I gave you is a flat response for higher quality sound.  I believe in power to provide the SPL, not manipulation of the response curve.  He should be thinking about trading up in amplifiers for these two subs for rap.

another question or 2. (by the way thanx stevdart). since his amp doesnt have a subsonic filter, would the best option be for a 30htz high pass f-mod? and because the truck is a single cab, i can't make the box  very deep which would elimintate the option for a long port right? or would i be able to bend it or sumthing? This is my first ported box project.  blah blah blah blah

what about 2 ft^3 with 3 x10 port @ 29hz? cuz this kid doesnt really care much bout sq, he'd rather be a blockrockerblah blah blah blah

Using the f-mods would be the smart way to go.  Yes you can put a bend in the port or even allow it to open on the side to make it fit.  The size you listed should work out fine.  With the tuning freq below the subsonic filter cutoff, you won't have problems with losing control of the cones below tuning frequency.  So make sure you use the 30 Hz f-mods.