No holes. Make it air tight, or close to it, and don't worry about getting fresh air in there. I used to incubate corn eggs in small ziplock sandwich boxes that were air tight, and I'd only open them every 2 weeks or so to check on them. It's the same for leo eggs. I use air tight 6oz plastic bowls, and only open them when I see that they are hatching. Same for BPs. 6 qt, practically air tight boxes that I only open every couple of weeks to see how they are coming along. I've never had any eggs run out of air.