Guys, some rust thru top corner of trunk, between rubber seal and then where 1/4 panel meets corner of rear window. Real awkward place. So, idea is to cut/shape new metal to weld in and do my best to copy other corner for shape? What gage metal is best? First time doing this but need to do this as well as patch repair bottom of panel. Lap or try butt weld? Won't be show car but still want to do a great job. Thanks.