I use silicone treated gun socks to store firearms in my safe.
These tend to repel moisture.
I've also started making my own out of a lightweight sweatshirt material (cotton blend) that I silicone impregnate using a spray silicone.
Note that you have to be careful with silicone since it can adhere to a firearm surface and can be almost impossible to remove. The socks are designed to avoid transfer of the silicone from the cloth material to the firearm.
I've seen analysis that indicates they will help a firearm inside a safe survive a fire. Here's a testimonial:
https://www.youtube.com/watch?v=Ag5Qk5S_ooU
Marc
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.