Many spot welds, no continuous welds as is often incorrectly implemented. For a good idea how to. check out "weldingtipsandtricks and V8TV on youtoob. Very informative for the beginner.

Cut back to solid metal, make the panel fill the hole with a 1mm gap, clean every God damn thing in sight, be patient, don't lose heart and enjoy the day.

Hope this helps and good luck with your project.