Just put a heat mat under 2/3 of it (where they hang out in the eggcrate but not under the water crystals or it will dry out too fast.) They prefer high humidity which is the challenge, I spray the eggcrate a couple of times a day. If it gets below about 75 degrees in the room I also suspend a ceramic heater in a clamp lamp above them .I move the lid to one end so it is not near the lamp of course.
No matter what you do they don't breed as prolifically in the winter but just wait till summer!
I personally find it easier to have 2 bins, I move the newborns to the feeder bin, grow them there and feed them off
and keep the adult breeders in the other.