Here look at this thread by me. I posted pictures of my new incubator and all the egg tubs have the substrateless grate in the bottom. Some member here use a type of lamp coil in place of the grate as well. As long as it supports eggs and sits on top of the substrate, either will work.
Foschi...so in each of your sterlite tubs there is a small layer of hatchrite (or whatever you are using) on the very bottom and the grate is on top?
Yes that is what substrateless is. Incubating medium on the bottom with the light diffuser on that. This allows for a more soaking medium without the eggs getting wet, which in turns keeps high humidity.