I've had people bring rifles and handguns to me for repair or accurizing, placing them in a gun case that had been in their relatively damp basement, then in the car trunk in the hot sun.
It only takes a few hours under those conditions to leave a thin layer of rust over the entire gun!!! No; don't store guns in gun cases unless you're sure ambient humidity levels are under 50% for the entire time and there are no wide variations in temperature.
“God save us from people who mean well.”
― Vikram Seth