Very likely, there will be internal pits on the outside skin. You may burn thru when welding at the seam, but you should be able to get it fixed up. You should consider sandblasting first before attempting repair. That will show the true nature of the rust extent.
I don't know of an inner door patch available, which would be your best option if you can find one.

Good luck.


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.