Don't put them anywhere your bps could touch them. My large ones get up to 165 degrees, and most of my others have a high of at least 130. Before I had my bater I would stuff the hand warmers between the tubs, that way the snakes couldn't lay on top of them. If you have a cooler or an old fridge it's much easier to keep them warm. I can keep my bater-a fridge at ~90 degrees for 8-9 hours just using gallon jugs filled with the hottest water I can get out of my tap. One thing you could also do if you don't have a cooler or fridge is use the hand warmers and fill water bottle with hot water and put them in the tubs. You need to make sure those bottles aren't any hotter than 95 before you put them in though.