The "air tight" wouldn't work either because the fire would go out.
I am really having trouble explaining the "doneness" of my chicken--and it may be size and kind of chicken. The chicken IS done and brown and good--and actually can be eaten exactly as is. But with that type of smoker and perhaps the steam/water, the pockets of fat sort of "congealed"--they were cooked, but still there. It happened with ribs also. They were done, but not (totally) fat rendered. So, in re-heating (a necessity anyway), the fat renders. If it is working well for everyone else the way they do it on their smokers, then my "addition" is not really cogent for your use. It's still really good.
With the side firebox, the effect does not seem to happen. I don't use water, or at least it isn't in the same proximity as in the small one where the contents of the smoker are right over the water all the time--and the water is boiling hot all the time.
And the beer can method may be the reason. I have really never cared for that particularly so don't do it.