http://www.homebrewtalk.com/f51/ge-7-cf ... on-192208/TomSD over on that forum built his with the collar connected to the lid.
I just got the same freezer and built a collar that I attached to the top of the freezer rather than the lid. It was pretty easy to build this way. Gravity pretty much holds the collar in place, but I used a couple plates screwed into the collar and the holes where the hinge used to attach to the body in back to keep it from sliding at all before using silicone caulk to seal around the inner edge of the collar.
As far as the "hassle" ggltd mentioned above, the entire build process took maybe 2 hours of laid back work one evening. (And I am not some super-handyman either.) I wouldn't call it a hassle to build a collar at all. Attaching to the base rather than the lid just seemed easier for construction purposes. I don't mind lifting kegs and extra few inches. If I need to, there's a step-stool nearby anyway.