You can put the stat in the incubator. I have done it and have a buddy who is extremely successful that does it(he is one of the bigger boa breeders). I'm building a new incubator that I will be mounting the stat on the outside of. The only way I would recommend putting the stat in the incubator is if you are going to be using a dry incubator. What I mean by that is having all of your humidity in the eggs tubs not in the incubator itself. You don't want moisture to cause any kind of shorts in the stat.