I use any plastic contianer that will contain that particular clutch of eggs. I used substrate, but I've thought about using bare.
Make sure there's plenty of humidity, but you'll probably want at least a airhole or two. I tried cracking the lids sometimes, and sometimes cracked the lids and put a washcloth over the top.
For my big clutch of 11 eggs, I actually had no lid, but put a hand towel over it, and misted the towel(the clutch was too large for any container I could find, unless it was too tall for the incubator!). Every one of those eggs hatched a healthy baby too.
Containers for eggs are not real precision, it's something to create the proper conditions for hatching.