Try this with chips making smoke in the kettle. For a given setting on the upper damper, say 1/2 open for instance, close the lower damper till smoke just quits seeping out the the seam between the lid and the bowl. I like to run my lower damper to allow just a tad more flow than the upper damper flow will allow, so that I get smoke seepage at the seam. Does this fill the area under the lid with heat and smoke? I like to think so. If I sealed a kettle lid I would leave a small section open so I could do this anyway. I think wind blowing cold air in at the seam would be the biggest culprit, but the kettles don't leak enough at the seam to worry about that. My Chargriller is another story however. It has 1/4 inch gaps at both ends. Adjusting the dampers for smoke seepage at the lid bottom works the same, but even it smokes fine in warm calmer weather. The kettle blows it out of the water on efficiency for charcoal usage to produce a set temp for the same duration however. Just my opinion.