I am getting ready to build a smoker with a bottom mounted firebox. The top cooking chamber is a piece of 24inch pipe line pipe 1/4 inch thick and 3 ft. long. I plam on having a square fire box 18x18x24 mounted underneath and conected with three 2" pipes. I also p[lan on having a defuser plate approx. 4inches below the cooking grill. any advise would be very much welcome before I start this project.