I, too, use a Cambro polycarbonate container; however, mine is the larger size (measures about 40 x 25 x 25 cm). I took the lid to a shop that does windows and for 10$ they cut a “mouse hole” in one end of the lid: the dimensions were sized so when the lid is in place, it just leaves enough space for the Anova to fit. The result is that there’s very little moisture loss. The only “down side” is that there’s enough condensation on the inside of the lid that I have to beware about creating a small flood when I remove the lid.
All of that said, I only use my Cambro when cooking a large item or quantity of food. If it’s just a couple of chicken breasts I use my 12 L stockpot, and cover with a scrap piece of aluminum foil.