Get some RUST REFORM
Rust-o-lioum (sp?) makes a product called RUST REFORM. It actually reforms rust chemically to a black inert material. This comes in a spay can and works GREAT!!!! After you allow this material to dry for a few hours, you can spray it with a rust resistant paint and forget it. If you skip the RUST REFORM step, the rust will eventually bleed thru even rust resistant paint. I've been using this product for years on my pickup under carriage, metal trailers, you name it. it is one of the best things I've discovered in my many years of owning and maintaining vehicles of all shapes and sizes!
Days camping (2015)----88 days
Days camping (2016) ---110 days
2016 Wildcat MAXX 28RKX (33' TT), 2007 13' Scamp
2015 Ram Laramie Hemi
30 years RV'ing
12 different RV's