I use to hunt Afognak Island in nothing but rain and salt spray from the ocean.
Before I went, I coated my gun (I don't use stainless, I use blued guns) with RIG, never had a problem.
I do that now, prior to putting a gun in the safe, its gets a coat of RIG, every now and then I get them out and coat them with RIG.
RIG stands for Rust Inhibitive Grease
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071