Yes I am right there with you on the heat packs.
They don't always last the full length and you have to watch they dont get to hot. But that would help ya a bit. keep them in a tight space and heat pack them. Note!!! Read the heat packs.. They hit 100 deg and you can cook your snakes so please make sure you keep on checking.

I hope the best for you and your snakes.
If all else fails body heat from you will help.

I have been watching the weather over there due to I have a baby to ship when ever it gets warm over there again.. some day..lol