Well, since I wanted to preserve the freezer (in case we want to use it for something else), I didn't want to use caulk to adhere the collar to the freezer. I used 3M double sided sticky tape, that is removable. It is kinda like the thing they have for hanging pictures (that sort of sticky "tape", and it appears to be working.
I've redone my tubing (the tubes needed to be shorter) and and I'm going to install the distributors (after I get a couple parts) and hook up my CO2 tank to the freezer and give it a test run.