Hey,
I have two showcase cages. From showcasecages.com, yeah? I ran into the same problem. To fix this I put duck tape where I wanted to place my UTH. That way the UTH had a smooth surface to stick too. I had to do this for my humidity gauges as well.
The only other problem I had with these cages was that my female Mojave would get stuck in the small area just above the glass doors. So I went to Low's and got a 6' foam tube for .97 cents and put that up there so she couldn't fit.
Lucas