Let me start by saying I have little experience with this, but I use to use a corner of my basement, crack a window and use UTH set at 55. Simple and worked well. Extreme cold I'd check temps. Also a stat on lights will burn them out fast.
Some great advice I got was to make sure the snakes drink. Once a week or so, dip their heads in shallow water dishes. That was from Tim, when I had some issues with a hognose. Sure makes sense when you think about it. In nature it is not a constant temp. It may warm a bit, the snake gets a little active and will probably seek water. So check hydration periodically.
Other options:
A guy I bought collared lizards from in Tennessee used a fridge. Added vents and tweaked the stat. That's an idea if you can handle that.
One customer of mine has a shelf by a window, and lets the drape cover it. Again a stat with belly heat at what ever temp he wants. I'm not so sure that is a good idea? But he lives in an apartment, and you take what you can get.
I hope more people have more options.
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Thanks for reading.
Big Tom
www.herpzilla.com