I live in las vegas and we have really dry air here, too. What I do for my hissers is I blocked off part of the screen mesh in their lid to reduce (but not completely stop) ventilation and I mist the cage down once or twice a day and give them high moisture foods (melons, apples, oranges, things like that). I have a pair and probably 12-17 babies, and they've done well so far. Other people might be in a more similar climate and could answer your question a bit better.