Assuming you want to save the door. If it was surface rust and not rust bleeding through the seams from underneath I'd remove the door and then sandblast the area.
If you don't care much and just want to slow it down I'd spray something like extend at it and maybe that might do something for a month or two.
Grape, No I don't. I used to but not any more. You can never get a parking spot for a show car unless you get there....well a lot earlier than I want to. They also have really cut down on the show car space and that's what I am interested in. I'm not interested in going to Jefferson to buy a car nor do I like swap meets. Two years in a row I drove there with the 70 Camaro and they were out of spaces, even though I got there at 8:00 AM. They wanted me to park in a parking lot. No friggin way, ain't gonna happen with my car.
I like to go to Iola and try to make that show every year. The Feature cars at Iola (Woody's) this year were spectacular. Lots of junk there as well.
Will be going to the Street Machine Nationals in Minneapolis this year I think, since the Power Tour is all on the east coast. The Power Tour and the types of cars that attend that event is what gets my juices flowing. Lots of HP, very nice body work, and driven on the street.