Hopefully you'll be testing things out for a while before you put the pythons in there. Anyway I would put in some holes with a soldering iron let it set for a while and check the temps, humidity etc. If you need more holes add some. That's what I did for my tubs. As for back heat vs. belly heat I don't know much about back heat. I use belly heat though and I've seen most people use a heat tape across the rack for belly heat as well. I'm sure someone who is more knowledgeable will chime in though