I think you will be okay, a decent fire rated safe is fairly well insulated and the temperature inside doesn't swing that radically. If you open the safe up with a bunch of cold steel in it, moisture in the outside air might condense on your guns and cause rust so that is one thing to watch for. The golden rod is a good idea and will probably prevent most condensation problems. I use to keep my safe in an unheated garage and never had any problems but then again I live in a dry climate, especially dry in the cold months. Keep an eye on it and if you do see a problem with moisture condensing on your guns when you open the door (it happens in a matter of seconds if it is going to happen) then you might want to install a small heater inside the safe. A thin film of WD40 is an excellent way to protect gun metal surfaces and that should be part of your routine when you return a gun to the safe after inspection or use.