I grew up in Michigan where they use salt on the roads in the winter time. If a car was not rust proofed the body would rot away after a few years. There was a company called ziebart that was considered a top of the line company. I don't know what sates they are located in. But I had bought a new 1979 GMC pickup and had it Ziebated right away. Then I got lazy and didn't take it in for the periodic maintenance checks, It had a little bubble under the corner of the bed that the material did not reach, that corner rotted through and the rest of the truck was fine. When I moved to Co. I was surprised at all the older vehicles that were not rusted out.

http://www.ziebart.com/