A friend kept a large jeweler's safe, (known in the trade as a money safe) outside under a carport roof for several months, including winter. It was full of guns in soft cases (not common knowledge in his neighborhood). He didn't open the door for long periods of time, but it wouldn't have made much difference since the indoor temperature was the same as outdoor temperature. When he moved everything, all was fine. Just don't move the guns back and forth between different temperature levels without giving them time to settle down. A common gun safe is not a money safe, but I think the result will be the same.
