Originally Posted by X-Traction

"Rust Proofing" usually means a coating of tar-like stuff. There's no way it can penetrate all the nooks and crannies and seams of the body. So salty water gets into those places and can't dry out. This is much worse than not having a coating at all.

Rust-Chek and Krown spray-on oil-based rustproofing creeps over the metal surfaces and so gets into most places where you need it. It's a fairly messy process and aftermath, but not as messy as extensive rust. Apparently this process is being banned in some places due to the amount of oil that drips off for days. But I'd have to think there's a higher environmental cost to premature replacement of vehicles.