Ya I know all the concepts. I've used copper backers supported on jacks that set on saw horses across the width of the roof. I have what looks like a ladder that is arched to the contour of the roof with each ladder rung with a little bit of an arch to match the crown and that is all held in place with Clecos. I still have warping and I can't seem to be able to hammer out the shrinkage from the welds without making a mess.