I don't like open tops or having the heating and lighting outside on top. I've tried to do it many times and many ways, and it has never worked well for me. Its a compromise and I don't like the results I get with that method. Its better than a low sided sweater box or tortoise table, but still nowhere near as good as a closed chamber. A closed chamber with a solid top and all of the heating and lighting inside is far superior in every way. It is more efficient, so it saves money on electricity, it allows the use of lower wattage bulbs, which reduces carapace desiccation, and it creates a more stable growing environment, which is much easier to maintain correctly and it generates better results from the growing babies.What was wrong with my answer? Plastic bins have served me and my baby tortoises well for many, many years. No need to build something.
Have you ever done a side-by-side comparison? Open topped tub on one side and a proper closed chamber on the other? I'm talking about an open topped tub that has been closed in with foil or plastic or something, but still has the lights outside the enclosure creating that chimney effect. The difference in appearance, pyramiding and growth rate of the hatchlings is striking. Very obvious differences.