safe storage
Well, this has been a problem that has plagued man for centuries. Ever since the caveman looked for something to store his fine Rock with a Stick, man has needed storage. It really comes down to, where do you live and how much rust do you like. If you live in a moist area and leave a gun in a case like that, it will eventually get rust spots. If you live in a dry state, you have more time. Honestly, the best storage is in a safe, with a dehumidifier if you live in a climate that has moisture.
There are long term storage bags, sold by various places. Most are impregnated with Silicone, fine oil, or the fur from baby seals. I have heard of people using these "Gun Socks" for long term storage, but they may discolor wood or metal, maybe.
If you do keep it in a case, check it from time to time. Also, if you shoot it, clean it, put it away and clean it again a month later as escaping gases, oozes, oils etc can work themselves out of pores.
Hope this helps