A human heating pad, set on med to high (depending on ambient room temps). Most roach colony keepers use the sterilite or rubbermaid totes. Many use heat tape, I've seen pics of set-ups with tubs sitting on wood slats or bricks and the heat tape run underneath, others use ceramic heat emitters, low watt, mounted above the screen on bricks. I know Jane (zebraflavencs) uses these bins, and the way her vivs are built, she can set the bins on top of them, close to the heat lamps and hers breed fine (she has over 10,000 of them-talk about a lot of bugs! Thats why we call her the Roach Queen!). I chose to avoid the heat tape as I've never used the stuff before and wasn't comfortable with that idea. I've had the human heating pad on one end of the bins (the egg crates are verticle and pushed to this side, the food/gel on the other to prevent the heat from drying it out) and haven't had a problem. The first couple days after setting this up (especially that first day) I monitored the heat pad constantly, checking the bottom of the bins to make sure nothing was being damaged or melting. The heat not only provides them with that 85 to 90 F temp range, but, with the bowl of water gel and the sliced oranges I put in on small bowls, it also creates some moderate humidty (which they also need, just not high humidity). I originally considered an under tank heater, but was warned that they could get too hot and damage the plastic-and no way in Hell was I going to take a chance of burning a nice little escape route! From my understanding, if you use heat tape it needs to be a certain size and type, I've seen some mention flexwatt. For me though, the heating pad seems to be working great, I already have a ton of little, tiny babies, and noticed another batch of new, tiny, white babies yesterday, probably around 30 of those and theres already over a hundred others that are about 1/8th of an inch.