Today we just bought a small used upright freezer to use as a cave. I am fully aware that I need to buy a temperature controller for it to maintain set temperatures in the 45-55 degree range. That is a known solution. The big question, of course, is how to maintain the proper humidity.
I have an idea that I have not yet tried, but I would like to put out there to see if people think it might work--in other words, please feel free to shoot holes in this if you think there is something I'm missing:
You can get a small children's room humidifier for aroud $40 to $60. What if, in addition to the temperature control, I were to put one of these in the bottom of the freezer with a cord routed to a switch on the outside? Of course, I would also need a hygrometer that has a sensor on a wire that could go inside the freezer and enable me to read the humidity from the outside without opening the door.
Just turning on the humidifier long enough to bring the humidity to the right level and then shutting it off might do the trick. Since the humidifier generates heat to disperse the water vapor, the temperature control would sense that and automaticaly turn on to compensate and keep the temperature at the preset level. That should leave the right saturation of water vaopr in the air to last until someone opens the door or at least a good while when I would be checking the reading and briefly turn on the humidifier again to maintain the right humidity.
If I can find the right hygrometer, it should be possible to put something like this together for under $200. What do people think? I'm willing to give it a try if I don't hear any reasons that it won't work. I will of course report back on results.