r2m
Richard
It depends upon which direction the panel is supported. If it's supported with the channels perpendicular to the support, it'll hold an awful lot of weight depending upon thickness of the panel.Thanks, what kind of loads will it take before collapsing?
If the panel direction is parallel to the support, not much at all.
It works the same as if you were working with corrugated cardboard boxes. They fold very easy in one direction and not so easy folding 90°.
I would venture with a 1/2" - 1" thick, 48" x 48" sheet with three cross bars should have no problem holding a packed 85 qt fridge, large Pelican cases and anything else you can load to the top of your interior with.
See if you can get a 12" x 12" in different thicknesses or something small to do some testing with.
You can frame it with T-slot aluminum extrusions. Amazon.com : t slot aluminum extrusion - https://www.amazon.com/s?k=t+slot+aluminum+extrusion&crid=36XPQW6GNZF3O&sprefix=t-slot+extrusion%2Caps%2C182&ref=nb_sb_ss_ts-doa-p_1_16