Arch repair panels

[general lee]

i dont have any experiance of it, but if the arch was tack welded along the joint before it was fully welded it probablly wouldnt warp, also if long continous welds were avoided the metal wouldnt get the heat needed to allow it to warp. so weld for a small bit stop and take it up somewhere else along the line. the weld could be ground down after. preperation is the key to any bodywork so unless you did a bit of filling and sanding before i wouldnt try it out as my first job.
most spray painters wouldnt touch a job sanded by the customer because it might be uneven and when he sprays over it will show up.