I am something of a nut about taking care of my guns and have never had rust problems with one exception. Way back when, I would hunt ducks from a blind in the shallow waters of the Texas Laguna Madre. No matter how well I oiled the receiver of my shotgun, it would have a fine coat of rust at the end of the day.
I solved the problem by giving the metal a coat of Liquid Turtle Wax car wax. No problems after that. I have also done the same for hunting rifles as well, if it is damp or raining at all. I don't know how common this is, but it worked well for me over the years.