I am making a patio smoker out a 20" pipe. It is 41" longplus the fire box, pipe is 1/4" thick. The concern I have is that the pipe is not exactly round. When I got it home I found that one end a oval shaped, other end is good. I am worried that when I cut the main door out it, the door might change shape and revert back to original shape. Any one have any thought on this?