I have been in many basements to have a peek at friends new firearms. Some nice finished basements some unfinished and full of ancient tools and lumber. Some that were more like a monks cell.
What ever the space is like, where you keep your firearms, make sure you have a dehumidifier there.
The picture on the right is a dehumidifier designed to go right inside your gun safe.
I recommend you dehumidify the room and inside the safe. The dried the better.
You would not believe how fast steel case ammo will go bad in a humid room.
--You do NOT want to find a glaze of rust on your favorite firearm!