Ok, the box is 16" x 14" x 18.5".
First, subtract the thickness of the MDF from each dimension, so that would make it 14.5" x 12.5" x 16" internally. Multiply all those and divide by 1728, and thats how I arrived at 1.67cf.
So, according to the manual, the port is 2" x 12.5" x 43". To account for the thickness of the wood in the port, add .75 to the width of the port, and you get 2.75" x 12.5" x 43". Multiply all those, and you get .85cf.
Subtract .85cf from 1.67cf, and you're left with a .82cf box for a sub which wants double that.
FTL.