Oil has a high vapor pressure and will be gone in a few months.
After that it is a question of dew settling on cold guns.
If you want a rust war laboratory, try keeping large surface grind cast iron in an unheated space near Seattle. Like a table saw, mill, lathe, shaper, drill press, band saw, etc.
Cosmoline has components that evaporate, but some don't. What is left is hard clean. It is easy to clean if it is a recent application:
https://en.wikipedia.org/wiki/Cosmoline.
If one can keep just a couple degrees above ambient, the dew will never settle. In 50 years with an unheated but attached garage with concrete floor, we had enough heat leaking through the walls to keep any rust from ever forming on a hammer. One night in a dirt floor unattached tractorhouse will make a hammer rust.
But a mill would easily rust in that same garage, having enough thermal mass to stay cold as warm wet air moved in with the weather. One solution was to cover the mill with an old sheet. This reduced circulation until the mill warmed up.
Guns are more like the hammer. All they need is a couple degrees above ambient and they do not rust. Thier stock will form mold first. Air circulation or a couple MORE degrees will prevent mold.