How to keep a stable temperature and humidity for an Asian water monitor enclosure?

I am planning to build a 12'x12' water monitor enclosure but I have run into a few problems. I cannot put the enclosure in my house, so I need to build it outside but I don't know how I am going to keep stable temperature and humidity with an outdoor enclosure. I know the temperature and humidity requirements I just don't know how I am going to accomplish it. I live in Alabama and it doesn't get terribly cold here. I know I will have to use good insulation for it and there is already electricity where the enclosure will go, but I don't think that will be enough to provide a stable environment. Any suggestions?

I had a similar situation with a savanna monitor and i live in Florida. His enclosure was completely open to the elements, so there was absolutly nil on the stabilty. I had something that resembled a low dog house that connected to the encosure with a heat lamp inside. This way no matter what the weather he had about a six by four space (he was about a foot long) that was stable year round. Then he could run amuck outside and always return to his house when he got too cold. He spent the entire summer outside, didn't use his house once until late fall. Just something to consider, its hard to stabilize such a big space as you have.