Blankets, Christmas lights wrapped up on top or a heating pad for your back, some bottles of hot water, electric blanket you probably have something around that gives a little heat

How cold is it going to get and how long will it stay at that temp last night was 22 degrees for the low here but didn't stay that way long and the outside worms were fine although they went deeper in there bin Worms are pretty tough if you can't get heat in there they will take some cold not an extended freeze but up until the point where the soil gets crusty on top from the cold most will survive if the box has enough material in it