Our Airstream also developed a crack over the door. The factory service manager told me that it is a common problem. You'd think that after 40-50 years of building essentially the same trailer Airstream might have fixed this by now. I'll bet that the 1965
Volkwagons didn't have any of the recurring problems that the 1950
I had visions of replacing the entire side of the trailer, with windows, a door, decals, and sundry expensive add-ons. The service manager suggested a patch that extended from the top of the door to the roof seam. It was a fraction of the cost I had been imagining.
The patch is obvious to anyone who looks for it, but it doesn't look bad. For the thousands of dollars saved, I think it looks great.
The factory did good work and saved me quite a bit of money.
Good luck with yours.