I've found with my firearms collection that anything coming into contact with metal surfaces must be of natural fiber construction i.e. cotton or wool. Anything made of plastics, foam (form of plastics), silicons, teflon and other man made products tend to cause/promote rust especially the foams. Foams that are approaching forty years old will crumble when touched. I've found foams made recently that are doing the same in less than five years. Probably has something to do with enviromental drive and bio-degradability. The breakdown most definately is not good for firearms long term storage.
Most of my firearms are stored in gun cases from Cabelas made from cotton duck canvas with a quilted cotton interior, brass zipper and leather trimmings. Since I began using this combo have not had a single firearm damaged either by rust or handling during transportation to gun shows where I display portions of my collection.
My gun safe was purchased at a going out of business hardware store sale. It was an old double door safe about three feet wide by two feet deep and about six feet tall. It will hold nearly a hundred pistols, rifles and shotguns when packed right. What most individuals don't understand is there are ways of placing firearms in gun safes which will double and potentially triple the storage capcaity over the manufacturers claimed capacity.