I don't hatch in cartons, I live in the desert- it is cold here. indoors we have a woodstove going. I have nothing that checks for moisture. but when I dry hatch they still come out just right.
just a tip. stryrofoam really holds in moisture, (doesn't breathe well) if you have 2 flat pans of water you have (I think) to much surface area. they say have a smaller surface area- deeper water container. like if you had an extra small plastic water bottle with a small (soda pop) top opening...