Heat packs and insulated boxes! I lost power last winter for 73 hours and it got really, really cold inside...like low 40 something. I packed the Leopard geckos in Rubbermaid bowls and put them in their shipping boxes (thank God I had the foresight to save them), put the Carpet pythons in pillow cases and popped them into an insulated box I had saved from a rat shipment and just put the tortoise in another rat box with a lot of newspaper. Tossed heat packs in and stacked them all up in the dog's crate then covered the big pile with blankets. I checked on them daily and changed the heat packs as quick as I could...they all survived. They were cold, but they were alive.
By the way, anyone know how annoying tortoise claws are on styrofoam...for 70 some hours...non-stop?? hahaha