I have had similar problems. More ventilation is all it takes. It depends on the tub size and the size of the water dish you're using. Using a smaller water dish can help keep humidity down. Instead of filling water dishes with warm water, try filling them with cooler water. It will warm up to cage temp, just as warm water will, but not as much will evaporate.

For my BP's large tub, I have 6 holes I made with my largest drill bit. For my BSTP's tiny tub, I have around 20 holes drilled with the same large drill bit. Both cages have the same humidity levels (around 60%).