I used the 2x8's from Home Depot. I borrowed a friend's planer for the rough work. This save a ton of time with the palm sander. Sanding went really fast, just a med-rough grit, then medium grit and called it good. I filled any cracks or knots with stainable putty, then stained, and used about 6 coats of poly urethane. Turned out really nice I think.
I've seen the double hinged setups. They look really nice, and maybe I'm missing something but I don't see the advantage. 8" is isn't that much to lift a keg over. Plus if you do lift the whole collar up, you'll need a helluva lot of clearance between the back of the keezer and the wall. Not a problem if it's in the middle of the room, but mine is up against wall and I need the room.
The collar I built sits right on top of the freezer, no glue and no caulk. The collar is really heavy and doesn't need to be physically attached for stability, it works just fine as is. Good luck with the project, you will love it when you're done.