Preheat an outdoor grill to 400 degrees F (200 degrees C). Place turkey into a roasting pan with the breast facing up.
Bring water to a boil in a large pot. Stir in butter, seasoned salt, pepper, and bouillon cubes until butter melts and bouillon dissolves.
Draw 30 milliliters liquid into a marinade injector; inject all over turkey. Pour remaining liquid into the bottom of the roasting pan. Cover the pan with aluminum foil.
Bake on the preheated grill, basting every 30 minutes, until no longer pink at the bone and the juices run clear, about 3 1/2 hours. An instant-read thermometer inserted into the thickest part of the thigh should read at least 165 degrees F (74 degrees C).
Remove turkey from the grill, cover, and let rest in a warm area for 10 to 15 minutes before slicing.