All right I have had a crack at it, but I'm tired and going to bed so if anyone sees any mistakes then correct me.
I worked on a 3 cubic foot box, all constructed with 1" MDF. With a slot port thats 1.5" wide, 13" high, at 35hz, which equals 10.654" length, which equals 0.2 cubic foot displacement including 1" MDF wall.
The Subwoofer specs say the 15" woofer has 0.14 cubic foot displacement.
So total displacement is 3 + 0.14 + 0.2 = 3.34 cubic feet.
A box that has outside dimensions of 36" x 15" x 15"= 3.3252 cubic feet, so given how tired I am will just have to do.
I have attached a diagram. It will be way out in the looks department because I designed it for a different box but the dimensions I changed and it will give you a general look of the box.