I keep a Coleman 5 day cooler on hand for emergencies. Haven't had to use it yet, but here's the plan:

Put warm water in the 1 liter soda bottles I've saved for that purpose. (reptile shipping heater packs would work too, but I have a gas stove and stored water I can heat if the electric goes out)

Bag all of the snakes separately and put them in the cooler in an open top cardboard box

Surround the cardboard box full of snakes with the warm water and close the door.

A 5 day cooler does a great job of keeping stuff warm as well as it does cold. I could reheat the water as needed if it gets too cool in there. I'm using one now for an incubator, they hold hte heat nicely.