The good news is that stainless tends to rust on the surface, almost like a film of rust, before it starts to pit. I have a live-aboard sailboat - trust me. It's impossible for me to keep all my stainless shined all the time. Yeah, there's naval jelly etc, but stay on top of it and it won't damage too much. Others may disagree, bit I've found that a wadding polish (no wax) called Nevr-Dull (sold at boating stores) tends to stay put and gently removes any surface rust. It also takes those blast marks off the front of the cylinder. Just keep it out of moving parts. I've used it on my S&W 686 for years, and that gun stays aboard the boat all summer.
I keep my semis vapor locked when aboard, as mentioned earlier, so my stainless 686 is the "go to guy".