How to fix sheet metal holes?

The most effective and permanent way without welding is. Take small pieces of flat metal and after cleaning the back of the hole on the panel. glue them to the back using JB weld quick set, After they dry fill the hole from the outside with the same and cut them flush with a razor blade while still soft. Works pretty good. Once they are cured you won't hit them off. Primer and paint right over them. You just have to make sure the metal on the panel is clean where you are gluing the little pieces to. I just closed up emblem holes in a hood for a guy that way. No warpage