The nitron finish should hold up pretty well. As good, or better, than anything else out there.
I lived in Florida when I was big into Sigs. Back then the finish rusted straight through easily and wore off pretty quick as well. Their optional "K-kote" worked until it flaked off in big chunks, and looked terrible as well.
These days, with the stainless slides and even the steel slides being nitron coated, you really shouldn't have much of a problem. That's some pretty good stuff.
I wouldn't keep in in a holster overnight, or leave it in the trunk of a car for a couple days, etc. Taking it out of the holster daily will allow you to give it the once over. Let it breathe and you should be fine. Don't neglect the internals. They are no where near as exposed as the outside, but humidity can get anywhere as you know.
If you have problems, and old cop trick is to use car wax on it. Car wax on a gun works the same as it does on a car. It just gives the environment something else it has to get through before attacking the finish, and the metal underneath. I wouldn't really expect much problems with the nitron finish though.