I just bought a gun safe and put it in the basement garage. I put a night light in it. When the inside temperature of the safe is warmer than the outside temperature, I am theorizing that rust will not be a problem. They make those heat rods for safes, but I am going to try the 99cent night light first.
Gary G - Your "night light theory" is good psychrometric science.
The 15 watts of heat from a night light is exactly that same as 15 watts from any other resistive heat source, and is more heat than an 8 or 12 watt rod.
It may be even better than a rod heater for these reasons:
When the heat is transferred off the rod by convection by adjacent currents of surrounding air, the heat gets distributed as far as the air will take it before it cools off.
A portion of the heat of the night light is transmitted through space by radiation to heat the surfaces that the light illuminates.
So the heat of nightlight may be distributed better than the heat from the rod.
Condensation is prevented when the metal surfaces of the guns are warmed to a temperature above the dewpoint of the surrounding air, and the nightlight does a better job of getting to more surfaces, with direct light and reflection.
The rod may not require any maintenance. The night light will require a replacement bulb every...well, I will tell you when I have one burn out.
But if I wanted to make a living selling a solution to rusty guns in safes, I would make more selling the sizzle of a unique-looking rod heater than I would trying to sell the same nighlight they have at the drug store.
Nice thing about lights is they come in all sizes.