Kracker - are you the guy I read about on WW that printed his enclosures? If so, that takes the cake for being creative. Very cool. This system sounds like it should pound pretty well. Using 4 12" subs is going to be tricky to get set up so they dont cancel out parts of the other speakers output. Where are you looking at location wise for these subs? There is a lot of academics you can read about in multi point canceling on the internet. The best advice on placement is probably to build a couple of temporary enclosure and place them into the proposed locations and fire the system up. I have a hunch you'll see some dramatic performance characteristics as those locations changes.

What are you thinking at this point...? 2 under the helm? and two in the observer locker? ported? sealed?