Normally diamond type enclosures are sealed, but can behave a lil like a 4th order. the only trye porteddiamond that I've seen was that Ascendant Astro with 12 18" mayhems, the ports were on each side, then the diamond with the subs were in the middle. Something like this from the front... IIII ...The "I"s representing the ports and the "" representig the sub baffles.
I actually thought about it for a second. I'll sketch my idea up real quick so you can see what I mean.