I assume the eggs aren't moved to the carton until day 18, right? Does it need to be cardboard or does it matter if it's a styrofoam carton? If you have used this method, did you have a good hatch? Better or worse than without it? I thought of doing this, but was worried the carton under the eggs might cut off some of the humidity that they need or something. I just thought advice from others might help.