I had a 41qt rack set up and honestly it was horrible. I fought ambient temps all the time, even worse in the winter. I had wrap it in 1.5" styrofoam from Home Depot to keep the ambient temps up. You can try putting more heat tape on it, but it just provides a warm spot not changing the ambient temps. I would skip any substrate and just use paper towels and go with a smaller hide. This will keep them temps up in the smaller hide.

I went with a T8 & T10 with RHP, best thing I have ever done.

Thanks,
Steve