subwoofer box question.

Look at www.proboxrocks.com   these guys have THE BEST pre-fab boxes I have ever used.

The are sealed with linex bedliner stuff......air tight, and tuff as nails

you can construct the enclosure with 2x dimensions but add a divider between each driver cell and count it in with your calculations.

hope this helps

One box or two?  You be the judge according to the room you have to work with.  If you made two complete enclosures there would be no reason to screw them together.  As the doctor said, one enclosure with a separator baffle.  Yes, each sub needs its air space.  The mfg was kind enough to give you volume that includes the displacement of the driver, so you figure each chamber to 1 ft^3 and you're good.  That cutout hole looks like 11" to me.

You must be making this box for behind the seat of a truck, as thin as it is.  See if you can push the depth back 2 inches and make up the difference elsewhere.  That's too close to the backside of the woofer.

 did some calculations

and a box for one subs comes out to

Depth = 7.2 inches

Height = 19.44 inches

Width = 12 inches

That's what you wrote.  The width is too small for the sub, the depth is not deep enough....just play around with the numbers and the room you have to work with to get a box that will fit the subs, give enough air volume, and fit the vehicle.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Hmm..  This sounds like a job for the good ol' Isobarik enclosure design.   .

Two subb mounted in one box with one directly behind the other with the airspace between them completely sealed.  This creates a constant pressure area between the drivers.  Overall, you will achieve a ~3dB increase across the entire frequency range of the subs, the low frequency extension should be lowered by ~1/4~1/3 octave, and you'll get the sound quality of a sealed enclosure.