I'm getting ready for a new 36x24x12 PVC cage to set on top of the one I have now, it will be identical to the one I have now. My cage has a RHP on the upper right rear of the cage. The new cage should be assembled in a few days. What I'm finding out is....I can set a Sterilite tub on top of my PVC cage that's setup with paper towel floor , hides and water and get very close to lower limit temps and humidity just from it sitting over top where the RHP is in the lower cage. Now it's got me wondering....If I stack another cage on top, is this going to be bad or good ? What I'm thinking is....I may have to run the upper cage RHP at a low temp to get the upper cage running proper. I may have to use a big air gap between the 2 cages if it's too much. I guess if it's too hot from below, adjusting the air gap between the 2 cages could help things out. The top of my lower cage reads 96 and I'm reaching 83 on top of the paper towels in the tub that's sitting on top. It's only been sitting there for 20 mins also. The cool side is 74.