I have NOT tried it, so be alert for mistakes?
when using car salvage, it used to be common for checking one dealer and they could then put out word on some sort of net of the long past age. they could list what they were looking for and other dealers could respond if they had it?
Seems logical that with the internet, etc. there might be a dealer setup to do that with RV parts?
Maybe worth a call to one of the bigger ones across the country to ask if that is possible?
But on the other hand and if I were looking at that price and that older RV, I might look at alternate! Like you mention, is it a good idea to spent a 1/3 of the total for a repair, if maybe some of the other parts are showing a bit of wear.
How big and bad and where that "door" sho0wed is a question but what about hiding it?
Some of my first RV were pretty close to total wrecks but a bit of thinking and accepting them as never going to be new, let me hide some pretty big defects!
A tree limb through the roof and patched was fine for a group of fishing guys!
Any chance of a bit of roof flashing, pop rivets, and caulk might make it work? A nice decal with something pretty to make it look like you planned the whole thing?
Sheet plastic of some sort, contact cement to place? Maybe a flat trim at top to hide the raw edge? Make something like a shower wall surround uses?
Maybe less trouble to "invent" than find a door?
For a discount of several thousand dollars, my wife and I will accept a few nicks!
If she wanted perfect, I would have been traded in years ago!