I put all my snakes into the incubator and fill the incubator with hot water bottles when our power goes out. You could do the same thing in a cooler or something of that sort. As long as you have a gas water heater you can keep your snakes warm easy and for free. Hand warmers get dangerous hot and can give off toxic fumes. I prefer hot water in bottles because they can go in an inclosed area like a cooler or incubator. Otherwise, if you only have a few snakes put them in a box like you would if you were shipping them with hand warmers taped to the top. I used to keep extra shipping boxes around for just that reason, but now I have far too many snakes for that.