SM1, I like the sound of it. Do you have a picture? If you cannot post pictures yet see my prev post on a workaround.

Are you saying rivet the aluminum top hat or square channel together to form the wall, or does it have to be welded, and then only rivet the 1/8th aluminum sheet to it?

Blakkmoon, would you frame out a wall in treated 2×4 ‘s? and then screw aluminum to the outside, and plywood and FRP on the inside? (like pic #2 above on my opening post?)..  assuming you go with a steel slab door.