It occured to me that people always use sheet stock and then add braces. Some do the B&W thing and add a honeycomb of sorts to fill and stiffen from the interior.

Has anybody considered emulating a "stress panel" - building a frame out of say 2X2s and then covering the outside/inside with something like 1/2" MDF. I guess the cavities could be filled with Great Stuff or similar (expanding foam). That would result in walls 2-1/4 inches thick - ought to be quite stiff, like a helicopter floor. The baffle would probably be solid, or at least it would be most convienient.