yeah that is empty space. My setup is not actually like that now. I actually turned my subs around and they are facing fowards now. And the boxes are together instead of having the space in between.Well if that current space in between your box (make a new box though) is just empty space, then there is room for your port. 6cu @ 32hz or w/e you want to do.
How many cubes would mine be if I made it just like my design above. After driver displacemenet, and the ports. Then of course the 3/4 " MDF board. I know you probably wont be able to tell me exactly because you wont know where the ports will be but give me a estimate.3 cubes should be sufficient.