For Turkey Neck Gravy I do a gravy drip pan below my Smoked Turkey while it is cooking on the smoker or grill. The benefit to the gravy pan isn't just for great tasting gravy - it's also to add moisture to the cooking atmosphere. During cooking the drippings from the turkey will fall into the pan and add to the great flavor.
You will need to restock the gravy pan with hot water so the veggies won't burn. When finished we will run the contents of this pan through a strainer. You should have 4 cups of juice left over. If not, then add some chicken stock to get enough. Bring the strained juices to a boil, then reduce to a simmer. Slowly add 4 tbsp of all purpose flour. Keep stirring. Remove from heat when it thickens. Salt and pepper to taste.