Safe sealant and belly heat?

[Sadieo]

Hey! So... I’m repurposing a set of old shelves as two leopard gecko enclosure, and another for my young ball python. And before I get started on making them, I’ve been doing lots of research on safest and best sealants and found butchers block food grade sealant and pond shield seem to be the best. Little bit hesitant on using pond shield because of the price and ratings seem to be low, people saying they have trouble with it hardening too quickly. On the other hand I’m worried about the butchers block not holding up in my pythons enclosure because of the humidity levels... Would it be a problem? Are there any sealants you’d recommend? Other people say house paint but I don’t feel like that’s the safest option. The other thing is belly heat... What is the safest way to do this? Needing to keep my pets warm but not burning them or causing fires? I know both questions have been asked a lot before, but I’m trying to find the absolute best for them. Thanks!