So I now realize that doing face2face clam shell allows for the smallest possible box and I will consider that. It seems though that I will not be saving that much space over the front2back design. When I consider the over all space requirements for the speaker, the only thing the clam design does is move the space requirements from inside to outside the box. Maybe I am missing something but isn't the only thing going to change, is whether I have cages or cones pointing out? Won't the overall depth of the sub assembly be roughly the same?
As for overall size, to build a "standard" ported sub with the same characteristics would require between 12 and 18 cubic feet. If I can get this built for under 9 cubic feet total then I will be very happy. And, my marriage will be happier also.
Trying really hard to understand basic principles of speaker building . . . . failing miserably.