door bows slightly outward at the bottom. The frame/jamb is fine though. You can check yours by holding a straight edge (piece of lumber - eyeball it to make sure that it's straight) but you will likely find the issue is with the door slab and not the trailer body/door frame.
I plan to rebuild the door someday and it looks like it should be simple and easy procedure. I expect that there's a (3/4"?) wood core sandwiched by the outer steel skin and interior paneling. When rebuilding day comes I will get a strong stable piece of plywood - possibly concrete forming grade, and new exterior door skin, about 3/32" from the bulk plastics shop.
The next step will be to disassemble the existing door and set aside all the hardware and metal pieces for reassembly. I'll use the existing wood core as a template, or a least transfer the measurements to the new plywood if the old wood is to rotten to handle, then reassemble.
To reduce the weight
I may swiss cheese the wood core with a series of holes cutout with a 3-4" hole saw.
Finally, to eliminate future detoriation I would take a hard look at the construction and installation of the door window frame and take measures to prevent any future water ingress/leakage from it - which I suspect is the smoking gun for any wonky doors of this sort of design.
But for all of that, if you could scan that rare and cool Ventura
brochure at a 300 dpi for the document center you would undoubtedly make other Ventura owners very happy - especially me.