A classic car magazine in Germany did a test of something like 15 different rust protection methods and products by making flanged steel boxes just like our beloved frame rails.

The boxes were left outside on the roof of their building for one year, and sprayed regularly with salt water. Protection methods ranged from naked metal to WD-40 and foam to more expensive and complex mixtures.

The winner hands down was Mike Sanders Rust Prevention Grease. I am not sure if this stuff is available outside of Europe, but here is one link to an English article on the company's homepage:

http://mike.british-cars.de/rustprevention.htm

I plan on using it in my 1800.

The box with foam in it was one of the worst. I also tried that method on an old CJ 5 I had once (when I didn't know any better), the sections rusted faster than without.

Graham