It depends upon where you live. You want to keep a dessicant pack or Goldenrod in your safe to keep the humidity in the 30-50% range, & you want the temperature to stay relatively stable. Wide fluctuations in temperature will cause the moisture in the air to condense on the metal of your guns, rusting them. Extremely low relative humidity (forced hot air furnace without a humidifier, or ambient conditions in the desert regions) will suck the moisture out the wood, eventually causing it to crack/crumble.

I would just lightly wipe all metal surfaces with gun oil, then handle with cotton gloves to prevent leaving fingerprints. According to the conservators at the Springfield Armory National Museum, wood does not need any preservative (many of their firearms are 200-300 years old).
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