+1 on not drilling holes in the freezer. I attached my collar to the lid using a construction adhesive such as liquid nails. I also used bathroom and kitchen caulk to seal the inside seams, even though I could see no light through them, just in case there was a draft. The collar is made of a sandwhich of two pieces of quarter inch masonite surrounding one inch foam insulation. This makes for a lighter collar than TWO-BY lumber. If you attach the collar to the main body of the freezer, you'll have to lift the kegs higher and risk banging your taps with them.
EDIT: Click on my gallery to see the pics. The seal is the original which I stapled to rock maple strip which lines the bottom of the collar. The blocks on the back of the collar are to provide backing for reattaching the hinges. It balances pretty well in the open position but you are still asking the hinges to do extra work and the foam core of the collar doesn't provide much support for screws.