Factory metal on my 74 is 18 ga. or .048" I used 16 ga on the rear corners of the tub and to block off the cowl vent. Everything else I have used 18 ga.
Nice work! Thanks for the photos. I will examine the extent further up, haven't ruled out separating the entire door. But I was thinking if it is not severe, with a bunch of pitting about to poke through, I would soak in phosphoric so it wicks between the panels and arrests the rust.
There...
I'm about to tackle a rusty area on the bottom of one of my rear half doors. My idea is to drill out the spot welds bonding the skin and the inner doubler at the bottom edge and cut out the rust below the radius between the corners. Fab an insert and weld. There is also rust between the skin...