What' s your definition of " extended period of time" . How often will you be getting them out, and wiping them down or oiling them?

If what you' re talking about is leaving them in the safe for over a year, without taking them out and taking care of them, I' d want 0 humidity level. It does not take long for moisture to rust carbon steel.

If 55% is the lowest you can get it, I would want to take my guns out at least once a month to clean them. Either that, or get silicone impregnated socks for them and store them in those.