I'd say just do a trial run and see if the UTH's will work. I can't imagine a UTH on top of another cage would affect the temps much, at least it doesn't with my leo setup (stacked sterilite drawers.) In my wooden cage, the wood was too thick and a UTH wouldn't have worked. I ended up investing in a radiant heat panel and attaching it to the ceiling, but this option would be too pricey in a three enclosure setup.