make a pattern in cardboard an transfer. it looks flat to the lip. should,nt be hard to do. i get flat patch sheets at the j/y, like roofs, van sides, hoods, trunks. on the inside lip contour make a cut carefully to butt edges and weld. you,ll get the hang of it. or spend the bucks at shermans. http://store.shermanparts.com/cgi-bin/sherman/product_list.html?img_num=305