Interesting comments. I have a trap gun I bought in 1982 and it has always been stored in its case. I have Win 101 in a retrofinished Browning case I've stored for 10 years. I see no signs of rust or any other damage from storing them this way. I also keep most of my guns in silicon impregnated socks muzzle down in my safe. That is more so to prevent damage from rubs, knocking together, etc. than to keep humidity off. All my guns are cleaned immediately after use and rubbed down with some type of rust inhibitor. I do live in a low humidity climate and never store my guns away if they have been in any type of rain, snow, mist, condensation. From my experience I think it depends on your climate conditions and how you look after and clean your guns.
