I second the Fliud Film and would use a good Hybrid Ceramic coating at a minimum, reapplied every 6 months.
When our trusty, rust free Chrysler Voyager van got kicked outside it was only 2 years before I started seeing rust. It sat those 2 winters without salt exposure at all during that time, waiting for our first kid to get his license. I think being outside accelerated the rust. Fluid Film would decrease that acceleration if also applied inside the rockers, cab corners and fenders.