I hope you will get through that storm alright and without loss of power !!
Hand warmers are a GREAT idea, but do not use them the same way like the ones meant for reptile shipping. They are different.
The ones for reptile shipping last a lot longer, but also don't get as hot. Hand warmers can get TO hot, so do not put them close to the snakes. You could put the snakes into pillow cases, then put all those into a big tub, put that tub into a bigger tub and tape the hand warmers along the sides of the bigger tub. Keep a thermometer with a probe ready so that you can monitor the temps in the smaller tub.
Well, that is one thing you could do, or something along those lines
Hopefully you won't have to, though !