I found a few of these at the local big name discount shop. They come two or three in a stack with one lid. I cut some egg-crate light diffuser to fit for the rack and a few smaller chunks of egg-crate as standoffs below the rack to keep it off the bottom and allow for air all around. With my cams, I try to keep enough moisture to keep a mist forming on the lid but not so much they form big drops. A wet sorta crumpled paper towel does the trick - off in the corner. I can get three cams per tray. When the GC/PC is developed, I pull the paper towel and just let it go in the fridge until ready to eat. Thanks to all the unnamed cf posters and their mini-cave designs!
The first pic shows the small mist/droplets on part of the lid. The second is a side view.