I had the same issue with a light skin on the dough balls and remembered a post, I believe by Gsans showing his method of putting a screw on wine top with a bit of water in the dough tray. I now put a small individual yogurt container with a couple tbs of water in my tray. Looking at the full trays of dough by others it seems unnecessary and impossible with their tight packed dough, but I believe it works for me.
I note that pictures of dough trays, as Omid's always look shiny, suggesting more moisture than mine though my hydration is 66%. Still having difficulty getting tight packed balls out of the tray but that's off topic.
Edit - I am using a birch ply dough box, not plastic