Hi there!~
I live 4000ft above sea level and we have stupid cold weather a lot. Because we're in the high desert, our nights always drop low even in the summer and we have about 65 days of frost free weather. Ugh.

I have this reptile cage: http://www.reptilebasics.com/2x3-Cag...h-p-16286.html
I have rigid insulation on all sides and the top. For you, using a radiant heat panel instead of flex watt would be good since it will heat the cage for the snake as well as keeping your ambient temps up without zapping your humidity. A thermostat to control the RHP is the other item you'd need. That's it!

I would encourage you to check this out and see if it might work for you and your situation