Going to be building a block/cedar smokehouse with a offset firebox. I plan on using block with firebrick lining the inside. I'm thinking about making my own door and vents. The firebox I have planned will be 18"x18"x16". I'm thinking of a 12"x16" main door and than a 3" sliding vent on the bottom. What thickness metal would be okay to use? I was thinking 3/16 as that's all the thicker I can weld with my welder but I do have buddies that have better welders if I need to go thicker.