to help with the heat until you have a uth maybe try getting a water bottle of some kind, and filling it with warm water. Put that near or next to the hide. TO retain heat in the tank, try putting foil on the sides of the tank as well. You should switch the water out as often as it gets cold, just make sure it's only warm to the touch.
Poor little fella...
It's real indication of a person, how they treat their animals. Good job rescuing it!