I smoke roasted a 22# bird yesterday. It took 2.5 hr.s and was done to perfection.
Just rub the skin with vegetable oil, put some aromatics (sage, apples, celery, etc) into the cavity. Place in a foil pan and tent with foil. Wrap the ends of the drumsticks so they don't burn. Load 25# of charcoal into your Weber Kettle and flame on. When the Q is hot enough to forge horseshoes. Add presoaked hickory, apple or cherry chunks. Put the bird on and close the lid. It'll smoke like crazy for about the first 45 minutes. Then every thing will settle down to a nice sizzle. If it seems too hot, close down the top vent to about two thirds. Make sure the top seals well or you will get too much air and incinerate the bird. Check with a meat thermometer after about 2 hours. You want to pull the bird when the temp in the breast is 175deg. Let it rest, covered with foil for 30 minutes before carving.
Enjoy