As for egg proofing, I'm not sure. I would assume smooth, large pebbles would work. I use egg crate and newspaper, so I wouldn't be the best person to ask.
For next boxes, I use 4-6 quart rubbermaid tubs with a hide box or something in them to make the cresties feel that there's a safe place to bury their eggs. My next boxes are a lot larger than what most people use, but I also have a very low rate of eggs laid on the newspaper.