That's awesome! I wish I had friends like yours!

It looks like putting up makeshift insulation will be one of your best bets. If you have free reign over the truck, and you're feeling ambitious, you could build a frame out of 2x4s and staple Mylar fabric to it for a wall. At least that way you'd have converted one big room into two for easier ambient temperature maintenance. It seems easier to get things warmer rather than cooler, so I'd set your temps around the ratsnakes and heat up the python racks as necessary. At least the temperature spread isn't insurmountable, a lot of people have pythons and keep their homes in the low 70s.

Here's what I found for Mylar, doesn't seem too expensive:
http://www.amazon.com/s/?ie=UTF8&key...l_99mnah0ny6_b

Best of luck!