Alright, I got a dimension for you.
If you build it this size, it will be very close to what they told you to use.
IF the 2 cuft was for the outside dimension and they took into consideration the wood and speaker then you can build it to this size
These are the OUTSIDE dimensions all in inches
12 inches deep
15 1/4 inches high
19 inches wide
which gives you 2.01 cuft
That same measurement, after you figure the wood gives you
10.5 inches deep
13 3/4 inches high
17 1/2 inches wide
gives you 1.46 cuft
Close to what I originally told you. PLUS that gives you more than enough room to mount the amp next to the box, since the amp is less that 13 inches wide.
Here is a quick picture ( if it helps)