First, with the latch closed, push down on the handle, and if there is any movement, it needs to be adjusted. Second, the top vent needs to be snug, but not tight, you should only need one hand to close it. Third, your gap in the lower vent could very well be your culprit, these vents need to be checked regularly, they can work open, and over time, ash can build and prevent a good closure. An easy check is light a fire, add smoking wood, and once you get good smoke, close everything and see where smoke is coming out. These grills take time to cool, but the fire should be out, overnite should be completely cool. Rob