I have a hygrometer and it never seems to go below 70% humidity. This is with two EvaDry's and a hot rod. Maybe I'm looking for too much but has anyone got an idea on what the best level of humidity would be to avoid rust, yet not dry out everything else, like holsters etc.
Thoughts?
I wouldn't be a bit surprised if your meter is not accurate.
It's not an uncommon problem with such instruments.
Take it outside and compare its humidity to a local=ish weather station in about an hour. That should give you some idea.
My safe is 450 Cubic Feet, and I have 2 Golden Rods that ,combined, are rated for 500 cubic feet. My holsters do not dry out, but my guns do not rust either. The only real problem that I have is with a Walther P22. The black slide turns a chalky white color. A good rub rub down with CLP will remove this "whiteness" but only lasts for roughly a week.
I do not know what the humidity level is in the safe, so I guess this post does not really answer the OPs question. Hopefully this gives you some info.