I keep mine well oiled. Same oily rag I wipe'em all down with after cleaning/handling.
I've left the old M1917's, 03's, a couple shotguns, etc. in zipped up vinyl/cloth gun cases in the attic for up to 8 years (longest they ever went without being inspected/wiped down) with no rust issues at all. The 3n1 oil was still shiny in some spots where the inside of the gun case hadn't made contacted and absorbed the oil.
I had some of my father-in-laws guns (deer rifles, shotguns) in the attic for over 20 years in their cases and got the down twice to inspect and wipe down. Again, no rust.
Down here it can be 0 F in the winter or 98 F in the summer and humid summer or winter. I've seen it so humid that even my cars sitting in the garage (and the tool boxes) would have a sheen of water drops on them when the temperature would rise a few degrees on a humid morning.
Keep oil on it, if you handle it, wipe it down again. I just shake my head when someone shows me a gun with palm prints or finger print rust marks on it and says, "Oh yeah, you've gotta have special stuff to keep a gun from rusting.
My 73 Laguna sat outside for almost 20 years (my oldest son is clueless about cars other than where to put the gas and he burnt up the starter after flooding it out one morning - moving it to mow the yard) after I stopped driving it. When we tore the 350 down to rebuild it as a 327 for my youngest son's Camaro the insides were as clean/shiny as the day it was parked. Pushrods, cam, crankshaft, cylinder walls, etc. looked perfect. That was just a 20 year old coating of Castrol 10W-40 - that no one touched with there sweaty/salty hands and of course it didn't rain inside the block but the humidity was whatever it was outside at the time.
Even so, about once a year I field strip, inspect, lube and wipe down a couple garage guns as these aren't there to be "stored".
