This was a big hit this past Christmas. A fairly easy mod to roast a 17lb turkey on my propane BBQ grill...
Step 1: Choosing and preparing your Bird
There are a couple of rules that you have to follow to successfully roast your turkey on a propane grill. First and foremost, don't get a bird that is too large for the grill! This is VERY important. When the turkey is on the rack with the lid closed, NO PART of the bird can be touching any part of the lid or sides! Make sure the you choose a turkey that will be at least 1.5 to 3 inches away from the surface of the grill on each side. My grill is a fairly standard model and I had absolutely no problems with a 17lb turkey. I could probably have gone as high as 20 lbs. If you have any doubts about what size turkey to get, just measure the inside of your grill's length, width and height and go to the store using the measurements as your guide. Be sure that you get a turkey that will be at least 1.5 to 3 inches SMALLER than your measurements on ALL sides (Including the TOP). Make sure that the bird is fully cleaned and pat dry.
A good second rule to follow is to not stuff the turkey with bread stuffing. Roasting a bread stuffed bird is possible, but it will add to the cooking time. What I suggest is to stuff it with some onion, apples, pears, and lots of fresh rosemary and sage. Just cut the onion, apples and pears into quarters and stuff them into the bird with the fresh rosemary and sage. Make sure to fully stuff it so that everything is tight inside. This will help the turkey keep its shape while cooking. Then, put a whole apple and/or pear on the end to keep everything in and tight. Here's a shot of my fully stuffed bird.
Once the bird is stuffed, make sure that it is tied so that the ends of the drumsticks are together and that the wings stay close to the breast. Note how I just tucked the drumstick ends into the flap of skin near the opening for the stuffing. I then just used string to keep the wings tight to the side of the bird. Try to make it as tight a ball as you can. Once it's tied, you can either butter the skin or keep it dry. I prefer to keep it dry because it makes the skin crispier.