Piggykins, we make this all the time. I'm typing it from memory since I don't have my laptop with me so bare with me a moment and let me know if you have any questions.
Take 1 Roaster Chicken - wash and drain. Do not pat dry as you need it to be wet for the seasoning to stick. We use Montreal Chicken Seasoning (but any chicken appropriate seasoning would work fine - even just salt, pepper and garlic. Rub the seasoning over the entire bird. Open a can of beer (or gingerale works great) and empty about 1/4 of the can. Sprinkle 1 tsp of seasoning into the beer.
Hint - do this on a cookie sheet and you'll have less mess to clean up.
Set the chickn over hte beer can (drumsticks to the bottom) and then carefully place the entire bird/can in the center of the grill over the drip pan.
For the grill. Set a drip pan in the middle of the gill bed and place a good amount of coals around it. Light the coals, and when they are ashen and ready to go, place the bird/can over the drip pan. Cover and let cook at 250*-300* for about 4 hours. Stick a meat thermometer in the thigh of the bird. When it reaches 180* it's done.
With very large tongs and oven mitts, carefully remove bird from grill and allow to sit for 10 minutes before removing the can. This may take two people to manipulate. Enjoy your chicken! Hope this is easy to understand. Let me know if you have any Q's
Shannon