I came across a paint called "Hammerite" and used it on the rusted lower sections of my 82 bronco to buy me spme time untill I can fix it. Well the paint held up for 4 years without any new signs of rust. Since then I've used it brackets and swim platform on my boat and again no rust. I now using it on the floor pans of my project. Not saying it's the only solution, but worth a look.
http://www.hammerite-automotive.com/
Carl