I have. On one door, I replaced the inside door bottom with a patch panel. On the other door, I made my own patch panels where needed (rust through). Both doors had small pinholes through the exterior skin at the bottom (showed up after media blasting). the rust was from the inside. I used a brass backing "paddle" and welded up the pinholes. The holes will open up immediately upon hitting with arc, but stops once you hit "good" full thickness metal. The backing paddle keeps the weld from building up on the inside of the skin. Its tedious, but can be done.
If the metal is so bad that welding just caused the hole to grow and grow, its time for a patch.
