I too am new to the Weber Grill and recently purchased the 22.5 Gold version of the grill. The first thing I tried on it was a beer butt chicken. I have made dozens of these on my gas grill. My problem was that the lid would not sit tight due to the top of the chicken sticking up too high by about 1 inch. Not a big bird either, 5 lbs. I tried both of my chicken beer butt holders and that did not help at all. Any ideas or mods?
I find coors cans are the perfect diameter(smaller than other beers) Sometimes I will need to rock the can to get past the back bone ridges then open the chest through the neck hole, and the bird will slip right over leaving just enough room(Just enough).
Also close the tops of those birds and tuck the wings in. By pulling the skin tight like this it helps with crisp skin as well.