I am neither a biochemist, nor a physicist, or anything related. But i have to say that some of the humidity cabinets shown in this discussion here do scare me.
I live in a wooden house in hot and high humidity climate where mold, especially in the rain season is a constant worry. In days of strong monsoon rains the humidity jumps to insane levels, and wood and leather is quickly covered in a thin layer of mold. It's especially bad in enclosed spaces, such as in closed cupboards, boxes, etc., where trapped moisture can't escape easily. That can happen within a day or so.
I have once discovered a few cakes of Pu Erh that i have forgotten in a wooden box for about ten years, most were OK, after airing them out for a while, but one in particular was completely off, and had a very musty smell/taste.
Open water and heat in an enclosed space without airflow, creating a tropical micro climate, can be a recipe for disaster. I think the numbers game here is a bit misleading, looking at exact levels of humidity, or temperature. Pu Erh's are aged successfully in many different climates. Hongkong, KL, or Singapore have quite different climates, but each has a history of excellent aged teas. But especially in KL and Singapore, being hotter and more humid, care has to be taken regarding mold (i have seen and drunken quite a bit of Pu Erh from there that was a bit too musty for my taste).
I believe that in a more dry climate it would be more important, and much safer, to find ways to raise humidity in the entire room the tea is stored in, than just in a small enclosed space, to enable more airflow and ventilation (that doesn't mean a heavy fan, just natural air circulation). That means in a tea storage room not to have aircondition, have a humidifier, and regularly air the room (as one should anyhow do).
Open bowls of water combined with heat, all in closed proximity to tea and hardly any air circulation might turn into a breeding ground for mold. I think that a healthy amount of air circulation is more important than desperately keeping humidity levels up to a specific number (and 70% is rather high humidity, and dangerous), especially when that number is reached only by having not enough air circulation in an enclosed space.