The only sure way to stop rust is to sand it out completely and paint it. Shouldn't be bad if it's like you say just surface rust. I've been building old cars for a long long time and rust...sucks! There are lots of products on the market that claim to convert rust to an inert state, I haven't found one that actually worked, eventually rust will come back. When steel oxidizes it changes the crystaline structure of the steel molecules, once rust has begun the only way to completely stop it is to completely remove it. With surface rust that means sand it till it's clean and shiny metal, prep and paint to keep future moisture out. I wouldn't put any panels or anything over it to hide it, the rust will continue to eat and if you ever do get rid of it the next owner will find huge honking holes under those panels.