Gooddaytoya!
40 Cal
You know, the temperature might be changing enough inside that safe to pass the dew point twice a day, unless the climate inside the safe is controlled by a thermostat inside it. Spyder Robotics sells the perfect thermostatically controlled systems for small spaces like that, that are powered with 110 volts. That would keep the air temperature in there within about 1° at all times so that dew could not precipitate. I doubt that safe is it all airtight and so let's in water vapor laden air as the air inside the safe expands and contracts as the temperature changes. Maybe that's something for you to think about. It could be a solution to that problem.I got a surprise the other day, I have always trusted barricade to protect my barrels. After months of rain and the purchase of a new Teslong bore scope I found surface rust in every one of my B/P barrels, back to 30wt motor oil or Rig gun grease for me.
As a footnote; I store my rifles in a gun safe out in a small utility room open to the garage, not in my climate controlled house. I have a safe heater rod in my safe that keeps the safe warm but apparently not enough.