ive not weld a cylinder before but im a welder  like jerry said the less weld the less it will warp i think the main  thing is to take your time fiting the peaces in so that when u weld it it only takes 1 pass of weld and to bolt it down to a true suface and preheat it and it shouldnt warp much if any at all Im geting redy to do 1 of mine im a little slow but ill post some progress pics