The purpose of the extension is to cool and clean the smoke. Your idea will certainly work by adjusting the length of pipe and controlling the air. but it would be more efficient to use a firebox of some type.
Below are some examples:
Now, how do we replicate the smokers of old in today’s environment? We start by using a remote firebox and pipe the smoke produced by your smoke generator of choice to the product chamber, which could be your smoker or a cardboard box, whatever you want to use. To cool the smoke as much as possible, the firebox is also being used as a heat sink, the more mass the better. The pipe used (preferably single wall stovepipe) to transport the smoke will also act as a heat sink so the longer it is, the better the results.
The above is an example using an Smoke Daddy Big Kahuna smoke generator in conjunction with a wood stove leading to a 22cf product chamber.
The above is example using a tray type pellet smoke generator inside a wood stove leading to a 22cf product chamber.
The above example uses a tray type smoke generator inside a mailbox feeding an MES.
The above example is using a MES cold smoke attachment feeding an MES.
Let us know how you do.