Do you think making a divider with some old box lids would be strong enough to solve this problem?
One reason is that here, there aren't many smaller boxes with enough height. I tried to use some plastic shoe boxes that look like your iris shoe boxes. They are only 11 cm tall, and when there is an egg on top of others it doesn't fit, or seems very close to the top and any condensation there. The next size up id almost double size box.