I have plastic boxes with hay in them as nest boxes. I could thin the hay down a bit, and place the ice packs underneath the box. If anyone doesn't have any horror stories to share about this idea, that's something I think I'll try right away. Also, have you found that it would affect the other layers? (She switches nests according to where someone has placed a lovely egg for her to sit.)I've done ice and it seemed to help but works better if you have plastic nesting material. It is more labor intensive than the cage.