Something for you to consider...
In the 1980's I purchased a stand up style freezer about the size of an average refrigerator. It has three large shelves, storage bins in the bottom and built into the door as well as a heavy duty factory door lock. I used it for many years and own it to this day. About twelve years ago my family moved and we put the freezer in the garage since we weren't going to use it. At first I considered selling it since it still worked just fine and looks like new. However, I had second thoughts and it now has a second life as my ammo storage container. It's virtually weather/water proof and fire resistant - it is an insulated metal freezer after all - and is heavy
(especially with umpteen thousands of rounds in it) for those that might want to carry it away. I keep a 25W bulb burning inside to help remove any humidity and unless you look inside it looks like nothing more than what it, a freezer. FWIW, since the door is always locked unless I'm doing something with it, that look isn't likely. I use my old freezer since it was available and already had a lock on it but a used/discarded refrigerator would do the job just as well. Also, while I keep my "ammo storage container" in the garage, any room will do (a basement or spare room) as long as you can fit it inside the space.
While the freezer is doing just fine where it is for now, who knows, if I ever decide to sell all my guns and ammo, I might just plug her back in and fill it up with ice cream!