I might get there, but for now I want to try it without taking off the bumper.
here is an idea: make a metal ring that goes around the rough shape of the hatch. This would be the main base piece and would attach to the lower hatch hinges. off this I would send out 3 supports going back. One dead center that would attach to the hitch. The others would be at the widest points of the tail, all angled in. they would all be attached along the way back (every foot or so) to make the frame. I am not sure what I would cover this with but the top part would be see through and attach to the top hatch hinges in the front and have some other attachment in the back so that I can open and close it for cargo.
My student copy of CAD ran out so no drawings
