I think a round, aero, pvc or sono would be easier to tune since the length can be modified more easily. I'm doing one round 8" sono tube. Its going to be around 4 cubes after displacements hopefully and be tuned to 32 Hz. Im making a temp box tomorrow for my subs, but ho[ing to start glassing later this week or early next week.
If all you want it the look and not the space saving benifits, then just build you a regular ported box and put a fiberglass shell around it. I've seen it done before and it'll look just as nice as a regular fiberglass box.