Doc, it depends on what I am smoking. If I am doing sticks I hang the probe thru the vent and about 1 inch below the hanger. If I am doing stuff in a rack then I run the probe thru the door (thin wire no harm and little leakage) and put it below the lowest rack. When you have racks in I would think you want to control the temp at the bottom so it don't get to hot. Racks that are loaded will block heat going to the top and if you have the probe at the top the bottom will be way over 20 degrees hotter than the top.