Using quite a few different calculators on the net, I came up with this...

I thought Net Volume was the Volume before displacement, but when I check the volume of this comes up to a little over 6cubes..allowing for displacement of the sub.. Thats not including the port of course. I can go up to 7 cubes(dont want to but will if I need to) but wanted to make sure this seemed right.

(Basiclly check my math...)

Also the total port area seems a little smaller than it should be...but im not 100% sure.

Its for an 18in BL by the way....and im looking for 6 cubs minus displacements and It needs to stay under the width and height specs..I can go a little longer on the depth...but id rather not(i could actually about about 40in deeper...but i travel and need the room)