Sub Box Dimensions For Ford F150

I just recently bought a JL 12w3-d2 for my truck.  I'm gonna power it with a Sony XM-2165.  Does anyone have any suggestions on what i should use for dimensions for the box.  I'm going to have it sealed using 3/4" mdf and I want it small enough that I don't lose any seat travel with a bench seat, and still have about 2 feet of space for my tools to sit behind my seat.  I'm going to mount the amplifier under the seat.

What does the paper work that came with the sub say? It should tell you the air space needed. Big Dave

I'm wanting to give it about 1 to 1.25 cuft of airspace.  I'm wondering if anyone has already built one for their F150 or someone else's.