Welding 101. Clean the base metal, before you ever strike an arc. Clean doesn't mean wipe it off with a rag ether. You need to get down to clean, shiny metal before you do anything else. Then you can fit in the patch, then weld after grinding off any slag, or scale. Your weld is just a bunch of spot welds. I'm not downing you, just letting you know the correct way to do the job. I would have buffed the whole part clean first. The removed the rotten metal, then ground to shiny metal, then make the patch, then weld it un place. Then prime and paint. That way, I know the repair will be there for a very long time. As for the gas tank, I don't like to weld on them, but it can be done if you perp it rite, and back fill it with a non flammable substance. When I was a kid, we had a neighbor kill himself by cutting into a 55 gallon drum with a torch. All in an attempted to make some BBQ pits to sale. I will never forget that. Most of the time, I repair gas tank holes with 2 part expoxt putty.