Water Jugs in Incubator

[sho220]

I'm setting up and testing my incubator for the first time this weekend and want to make sure it's working correctly before I start breeding the two pairs who are going to be old/large enough to go this season. The electronics all work (YAY!), but I have a question about the water jugs - do you screw the tops down tightly so they're just thermal mass to help keep the temperature from fluctuating, or do you leave the tops loose so that they help keep the humidity up, and you refill the jugs periodically? This incubator is a converted refrigerator that can hold 8 6-qt tubs with enough room on the bottom for 7 2-liter plastic bottles.

I've never heard of anyone leaving the tops off. Usually it's just for heat retention. I guess it couldn't hurt though, unless they tipped over...