The drawing below shows the design of a very good smoker.... The calculators, to do this, are in the thread... I would recommend following plans of a proven smoker.... You are going to put a lot of work into this project.... ....I have it sketched out with dimensions. My thought about the firebox to CC connection was to cut a 10x10 hole in each, and join them with a box a couple of inches tall with a damper installed. It matches up with Feldons calcs. I want to make rectangular vents for the firebox vice round ones. Easier cutting. I have an ashbox door from an old stove to install on the end of the FB.