Dennis,
I cannot answer you question as I have no means of checking humidity. I have always considered that hydration / dehydration is a issue with the species. So when I was maintaining a number of boas, I had a small pan of water beneath one hide. And I sometimes would mist the moss I had under another one of the hides.

But to insure hydration, periodically I would soak boas for 5 - 10 minutes in a jar with shallow water.

Richard F. Hoyer