I think it was in one of the Primary & Secondary podcasts that some former special ops were talking about extreme conditions, and one thing they learned from training in Norway was that they didn't bring their rifles into their tents. Because the temps are kept higher inside the absolute humidity increases, bringing the rifles in will condense that humidity into the action, and getting out again would freeze the weapons.
Also apparently if you change barrels on a machine gun while laying on a decent amount of snow, you have to have a shooting mat or else it vanishes.