Gun safes are not air-tight, so the keeping a gun in a safe as opposed to an unbreathable hard or soft gun case isn’t as risky in terms of corrosion. However, guns can absolutely rust inside a safe, especially if you live in a humid climate. The likelihood increases if you put your safe in garage or building that’s not climate-controlled. There are several in-safe dehumidifiers and rechargeable silica gel packs on the market that you should consider. Also, always be sure to clean guns and wipe them down with a lightly-oiled rag before you put them away. If you bring a gun in from the cold, condensation can form on it, so be sure to wipe it down even if you didn’t shoot it.