I store them in their cases too. In the Tau 7 case, thats stuffed with styropor others with foam. I dó clean off the barrel with oily cloth after use and once a year. Tau 7s are very prone to rust but even they do not rust.
If I have taken them outside in the cold I do let them lie with open case for a while to acclimatize to prevent condensatin and rust
I do not empty them nor release any cilinders except on the one's that otherwise slowly empty the cilinder themselves (tau again) . But walthers, morini, cilinder all stay on