I know that it's obviously not a good thing to have rust on your machines, and I do my best to keep mine from rusting. But when you bring up keeping your machines in a barn shop or something, people act like you are putting machines to their death. The humidity will probably create surface rust on the iron surfaces, but with routine maintenance, that should be kept to a minimum. And I think they're less common now, but I think barn shops are fairly common. Even if the machine surface does develop heavy rust, the only major issue I would see is losing the ability to smoothly pass through material.
I'm no expert, I may sound stupid, but I'm wondering if barn shops or any non insulated shops are really as bad for your machines as some say.