Here's another suggestion.
Not sure if it would catch fire, but that's what aluminum foil is for...right?
I think adding a ventilation hole to the firebox would be more beneficial. From my experience with the ECB, those things aren't sealed tight and have no problem with exhaust.
The ECB can present issues with the ash build up in the coal pan. For that, some type of hole to allow the ashes to fall would be advisable. I have used a coal grate that fits the tiny Weber Smoky Joe with decent success.