If there is much cooling, there will be contraction to some level.
In other words something is going to be moving inwards.
If the contraction isn't too much, you might suck in some water from the airlock.
I haven't cold crashed to clarify so I'm interested to hear what everyone else says. I figured on maybe doing the tin foil over the top, but I'm going to be using the same freezer that is my kegorator so there aren't any off smells in there.
Let's see if I keep this updated!
Black Butte clone
Up next.. Firestone Union Jack clone