[simulator5g]

This is basically a solved problem. Saturn used plastic body panels on cars for a while. These cars had some painted metal parts that were protected by the plastic, and would never rust, because painted metal only rusts after the paint is compromised. Saturn went bankrupt and no one has been doing this. I suspect that it is really bad for a car company's bottom line because it lets people keep their car instead of buying a new one.

Also, you can coat your car underbody in an oil based coating 1-2x a year, and it won't rust. Its just an annoying chore that most people don't want to even think about.