With my experience, you can simply a small bowl of water that fits into the ripening box with or without a damp paper towel or two to achieve the desired humidity.
I would like to share my experience with making swiss cheese. My problem is that i cannot achieve the holes in the cheese. My cheese is about 3 weeks old and so far no holes. The temp and humidity are either dead on or very close to the recipe (Ricki Carroll's...have not found another- if anyone would like to share, i would be grateful) and other than offering a very strong odor and producing mold, the cheese has not transformed much.
After doing more research, i have discovered that in order for the propionic shermanii to do its job, it needs a very large cheese mass. My recipe called for only 2 gallons and the larger home made cheeses need almost 30 gallons!!