I keep them on newspaper at all times and never had any issues. The only thing I do different is when they are getting close to laying I remove the water bowl about a week before they lay and only offer water when I am watching because they tend to tip the bowls all the time. So to prevent the mold or excess moisture on the eggs I just take the bowl out. I also change the paper about a week before the eggs are due and add an extra layer or 2 but they always without fail move all of the paper aside and lay on the bottom of the tub.