You said sealed right?
Build a nicely braced one... lemme find an example...
I'd show you my home sub but its kinda difficult to get the sub out, the rubber gasket seems to have glued itself to the paint. (the cutout is actually just that small.)
http://www.avsforum.com/avs-vb/showthread.php?t=1221102
This guys got the right idea.
LOL at 110 at 15 Hz though...