Where I live (Oregon) there isn't a lot of ground water, so everyone here including myself have 2500 gallon underground water storage tanks.
I built a shed over the top of it and insulated it. I have built a couple of shelves on the inside and have a remote out there that shows temp and humidity.
Seems the constant water temp of 55 degrees keeps the temp regulated and also keeps the humidity up at around 80-85%. Temp outside here is 30 but inside the "cave" is 47 degrees.
So now I have 2 Chedders, a Gouda and 2 Romanos that will make there home there. Wish me luck!