You don’t need a heat pad. Might be an unpopular opinion around here, but you don’t. None of my snakes have belly heat. (Burm, a ball, and a Suriname boa). Eventually they will all be radiant heat panels over head. For now the burm and the ball are utilizing heat lamps with ceramic heat emitters. Get some. The red light is said to bother them because they can see it. You don’t need Uv or anything so you can use the che 24/7. I compensate a little for the hide, so I let me surface temps outside of the hide get to 92ish. Also get better hides. Those half logs are said to be not great. Point of the hide is for the snake to feel hidden and secure. Those just aren’t going to do it. Your cool side is too low. Ideally you want 78-80. No less than 76 for sure. I don’t let mine get under 77.
my burm is in a 40 gal breeder cage right now too. I have 2 lamps. Both controlled by a herpstat. Cool side is at 80 warm side 88-90 air temps, about 91 floor temps outside of hide. I use 2 100 watt Che’s. Amazon has them cheaper than any store will more than likely. Paid I think $6 for mine.
I haven’t used belly heat in over 12 years. Mainly radiant heat panels. In a pinch right now that’s why I have heat lamps. Waiting on the burms animal plastics cage to get here. Already have the rhp for it. Ball I got the cage yesterday and all put together. But it’s the daughters snake and a Xmas present so it has to wait for that. Needs to air out from the sealant anyways. In all the years of not using belly heat, on anything from 3’ ball pythons, to 7’ boas, to a 13’ Burmese python...never had a regurge...never had an RI.