Sorry for thsee random stories, but your pictures triggers this stuff. My rear deck frame is just like yours. I made 3 deck panels. I have them locked in front with tabs that slide under the angle & lock down in the rear with jeep hood style tie downs.
Well, we were on highway doing about 70 & passed a semi. One of the plywood panels got sucked off from the vacuum blast! The hardware had stripped through. The ply landed in middle of road & we circled back to get it. No one was hurt or cars damaged so we were lucky there. Now I tie several straps across the rear decks when on highway, as well as made the latches 3x stronger.