DeMo180a,
Based on my having some exposure to metal work and finishing, You have received first rate advice on every single point including not storing it in the leather.
Some leathers have been and still are "vegatable tanned".
Hollis knows about a place near him that uses the tannic acid from Doug Fir bark instead of the harsh chromic acids that depending on how they are used could rust about anything.
Another thing leather does to cause corrosion is hold moisture in contact with steel like a plastic bag.

Bill that tannery is no more. Not sure what they are going to do with the old building, it is in poor shape.

One of the new (not really new) concept is vacuum sealing. We use it for food products, but I have seen where it is very useful for long term storage for just about anything else. Money, documents, etc.

A person could even make a bag long enough for a rifle. I haven't tried that. I have been planing or trying it with ammo and maybe a few pistols that I don't shoot much and want to keep.