I hate to share this, but 65 years of storing guns, in and out of safes in the DC area has resulted in no rust or condensation with no help from rust inhibitors. Maybe I'm just lucky. For several years, my only safe was on a carport, unprotected from weather and still no damage to the guns. I have never used a light or anything else. Now I use a dehumidifier and empty it daily, still no sign of rust or condensation.
Luck probably has very little to do with this, unless it is considered lucky to know enough that it takes a multifaceted approach to keep gun metal free of rust. Common red rust is ferric oxide (hydrate), and the only way to totally prevent it is to keep oxygen away from the surface of steel. That isn't easy when oxygen is 21% of the air we breathe. Bluing on our guns is a different oxide that inhibits the formation of red rust, but bluing alone isn't nearly enough. Over time, unprotected blued steel will acquire a brown patina, which is a nice term for rust. So I would assume that eightbore is lucky enough to know he has to use something that inhibits oxygen from reacting with his gun metal, such as wax or a good gun oil. I find it hard to believe he has never used any gun oils or products that inhibit corrosion, especially in a climate with seasonal high humidity. All gun oil is not created equal, and some last longer and do a better job than others. We have all seen the tests and debates about which ones are best. Products like RIG or cosmoline are great for long term storage, but a pain to remove for frequently used guns. You can store a gun in a very dry climate and still get a fine grained rust over time if it isn't properly cleaned and protected. Perspiration contains salt which is hygroscopic, and will pull in moisture, which contains oxygen. So merely handling a gun could cause rusting issues, which is why curators of gun museums handle them with clean white gloves.
The vapor phase corrosion inhibitor (VPCI) paper or plastic that Stan and I mentioned earlier is wonderful stuff, because it emits a volatile vapor that collects at the surface of steel, and displaces oxygen. But even that has limitations because the VPCI chemical infused into it dissipates over time, so it must eventually be replaced. Naturally, it lasts longer when it isn't exposed to heat and sunlight. When we recently installed a new Fanuc 6 axis robot at work, it came crated and nicely wrapped in Cortec VPCI plastic, so I snagged a few hundred sq. ft. that would have been discarded, as my co-workers were blissfully unaware of what it is good for.
https://www.theruststore.com/VCI-C12.aspx
