I found that, with just a little fiddling, square tube fits into a slot in the sides...
You could presumably omit the top bar if you wanted it open, though at the cost of some strength. Were you to do so, I would triangulate the bottom corners.
But weight was not a problem:
easily holds
The two things on the top were for a Hi-Lift.
Thoughts:
Obviously you'd have the most strength with the doors closed.
Squeaking can be reduced by using rubber on the bits where the doors meet in the middle.
Some minor notching was required at the top; see the first pic. Otherwise it just sliiiides right down, depending on how square you welded it

I drilled mine to match the nuts in the sides for the truck-style tailgate, so it bolts in as well as friction fits. While I wouldn't use it as an extraction point, it's certainly strong enough to hold even spare (even, say, a 39" or 42") and whatever else you wanted to hang there.
Anyway, some thoughts.
-- A