Well my ? is how are you measuring your temps? Next if you unstack the tubs what happends are they both to cool? With the same size uth on both they should stay close to the same. As for the water issue, cypress is what i use per my breeders recomendation and it can get damp without molding, i would try putting way less water in the bowl to start with since they dont drink much and your tub will hold the humidity way better so you dont have to count on it to keep up the humidity.