Two eye bolts from Home depot, and a long bar padlock work pretty well, if all you are concerned about is security. For the finish of the weapon, I wouldn't recommend it for vertical storage. String it horizontally with the eyebolts around the stock and something supporting the front of the weapon is ok, as long as you put up some foam or other insulation to keep the frearm off of the wall. You may want 2 eyebolts in the front as well, and another lock, if you are worried that someone could pry the weapon off by grabbing the barrel. But it works, and it's probably around 10 bux or so. Extra points for mounting all of this into a frame.
I think it may be betterin the long run to store the weapons where they can breathe. You could get a sock for them, but storing them anywhere where they could get damp and rust becomes a problem. Something to keep in mind. Best bet for security is a real safe. Dehumidifiers, etc, and the safe itself, and it really adds up price wise. Plus, it slows access.
But you do not want to leave the frearm within view. If you are in your house, and you are asleep, and do not wake up, the last thing you would want to see is a burglar standing there with your shotgun pointed at your face. Leaving it uncased and within view and this could easily happen. Plus, he's going to check the places where you might normally store one. In a closet, under the bed, between the matress and boxspring, and your gun will go bye bye faster than you can blink. You have to find someplace that he might not look. But you have to be able to access it quickly. It takes some thought.