Like Stalkingbear said, it's no so much the temperature change, as much as it's the amount of humidity in the air. If a glass of icewater is set on a table and condensation forms on the outside of the glass, then there's enough humidity to worry about. Here in Florida a gun that's taken outside from an airconditioned house will form a layer of moisture on all the metal parts. The best product that I've found is "Tetra gun oil", if it works here it'll work anywhere.