You could try a radiant heat panel: http://www.reptilebasics.com/RBI-Rad...p-1-c-283.html. They go at the top of the enclosure and really help to bump up the ambient temps without zapping the humidity.

I live in the high desert and we have no humidity. It is also cold. I have 6 RBI cages and have them all with RHP's. Works like a charm