Our guys humidity levels usually run in the 70% bracket, low 80's. Yes, I know this makes more work for us but we don't mind. During shed time it runs 80's to 90's. And we are in the desert southwest. Right now the relative humidity outside is 11%, to give you an idea of what we are up against.

With the Exo tanks they have air vents all along the front edge and I made glass tops with plastic grip handles on each one so they can be removed if need be. Without them on we notice about a 10% to 15% humidity drop within a very short time.

We have run them like this for years - never any molds or scale rot and best of all no URI's.