Safe have a hole out the side / bottom for 110? Can you drill one?
I put a small light in my main safe, with the expensive guns, and I get great humidity reading year round.
You want proper humidity, not zero humidity. To low, and the wood dries out. Cracks, gets brittle, shrinks.
According to the NRA:
50% humidity at 70 degrees is considered ideal "Arms Museum" storage conditions.
You can get a temp and humidity gauge, that monitors highs and lows, to keep tabs on averages.