Unless you totally forget about a gun, once cleaned and checked every couple of months, breakfree or Hoppes will keep a gun rust free. A swamp cooler is nothing like living in the south where humidity is a way of life, and when I lived where it is humid, with guns, they were fine and I lived in Louisianna, Alabama, Hawaii and Tacoma, Wa, all without a problem. Forgetting about a gun is the mistake, just check it every couple of months. Set your Outlook to remind you to check it every couple of months and you'll be fine.
Shes lasted this long, she's not a puppy, she'll do fine,
Ed