In my personal opinion, I'd sell it and get myself something else (like a PVC enclosure). Depending where you live, you're going to have a hard time with temp fluctuation and keeping up the humidity.

With that said, I think belly heat is overrated and completely unnecessary. I know that it's suggested on the forums all day long but all commercial breeders focus on maintaining solid ambient temps. I've also only provide ambient temps of 80-82 and never had an issue. If I was in your shoes, I'd focus on providing ambient temps of 78-82 and work on your humidity.