Learned the old gun case lesson a long time ago, but if you must keep them in a gun case you can greatly prevent the rust, by first line the case with a 100% cotton flannel fabric, Walmart sells a baby blanket material that works fine, but about any fabric store will have some, also for handguns buy some 100% cotton socks and store them in there inside the lined case. Now if your case gets wet or seems damp you need to dry it and make sure that it is dry before you close you guns in it.