Bobby_M has his collar attached to the lid. If you use a fairly lightweight wood for it, you'll be fine, since the hinges will have to hold up the extra weight. It also allows you to use the same screw holes in the back of the freezer body.
You'll have to remove the gasket from the lid, at least, and attach it to the bottom of the collar.
If you're pretty good at DIY, go for it. I'm not, so I attached the collar to the freezer body and put the lid on that. Plus, I have a big keezer, so I'm not sure the hinges could hold such a large collar.