We keep Rhino vipers for a very long time and have made very good experiences by keeping them dry not humid.
Young ones need to drink allot but the humidity does not seem to need to be high.. in fact high humidity is nod good according to our experiences.
Temperatures should not be too high eighter. Keep the cage at room temperature with a small spotlight in one corner so they can bask if they desire.
In short.. keep them not too warm and relatively dry.
We give ours an overnight soaking in a container with 1/4 inch water every few weeks for them to absorb/drink enough water.. this is good specially before shedding.
I have had no losses at all in the last 2 years on my rhinos and I keep quite a bunch.

Price Reptiles International