When we lived in Michigan and Nebraska I use to spray the underside of our cars with the used motor oil, at every oil change. Keep it off the rubber parts and coat them with silicone spray. That was in the winter. In the summer we kept the underside of the car clean and repainted anything that needed it. The result, zero rust, in spite of the road salt.

LOL, I know I'm too anal about that kind of thing, but I think at one time I had the only rust free 850 Spider in the US.

You *could* brush the rust off and apply a little paint.