As for geometry, just sturdy wood was support enough for us last year. All we did was put a smaller, inset rectangle of 22 on the plywood sides that opened, and they fit snugly inside of the larger 44 frame.
As for sealing, all that we needed last year was a simple hinge-locky-thingy that was on each of our movable sides.
DO NOT! DO NOT GO OVER 400LBS!!!
It will coast you BIG time at the Event!
This is the voice of experience (all BAD, can you say $$$$$$$)
FEDEX has a limit,
Freeman decorating charges by the POUND, at each Event!
we are going for 375lb