I think the humidity is more damaging than cold. I moved into a stone cottage in rural Limerick, Ireland, and have lost a few pieces of kit. Humidity here averages 75% minimum sometimes reaching into the 90%. Stored for a long time the power caps discharge completely and then draw huge amounts of current at switch on. When I moved country I sold a lot of stuff including my variac which I used to slowly bring equipment up to voltage.
In future I will do as @puptent suggested, vacuum bag the components but only after leaving them overnight with a dehumidifier running.