Very hard to tell exactly what is going on without detailed pictures, but I think I have the basic idea. I can only guess, but I'd have to assume cutting notches to allow for folding would work, but would weaken the floor. Metal bracing bars would be an option, but it may require a lot of time hunting for the right salvage piece(s) or fabricating your own. Metal is relatively ductile, so it isn't very strong against bending forces. A piece of sheet metal would be basically useless without bracing too. Bracing bars are often bent into a U or V shape to increase their strength and you see this a lot in cheap shelving braces and other metal work. Maybe some corrugated metal would work for the same reason, but I don't have any experience with it. Shelving braces might be a good source for you. May be able to add them to what you have after you cut the notches and be good to go.