In their incubators. I have found some narrow trays with open sides but the bottoms are solid. I couldn't find any with open bottoms. My husband has offered to try to drill holes in the bottoms but I wanted to find out if any of you use them with solid bottoms? If not, what do you think about putting something fluffy in the trays to get the eggs up so the air can circulate around them? I am afraid that the trays might be too brittle to withstand being drilled.