Remove turkey from brine and pat dry. Carefully separating the skin from the turkey, spread the butter under the skin on the turkey breast. Continue spreading butter on all places you can get under the skin. Season turkey with salt and pepper. Place turkey in roaster pan and stuff the cavity with the onion OR with options suggested in the above post.
Leave grill on Smoke and place turkey in roasting pan on the grill and smoke for 2 1/2 to 3 hours.
Increase grill setting to 350 degrees and cook for additional 3 1/2 to 4 hours, or until the breast internal temperature reaches 160 degrees F.
Remove from grill and let rest for 15 minutes before slicing. Enjoy!