As to the blowing holes, don’t be so quick to turn down the heat, I would first adjust to a faster wire feed setting and then adjust the operator to a shorter duration on the trigger pull. A faster, hotter weld tack will give you flatter weld with better penetration. So in essence the quicker on-off of the trigger pull gives you less heat without sacrificing weld penetration. See the “MIG welding tips and tricks” sticky at the top of the page for more Info.
For fixing the tailgate in the video, it is only going to get worse with time and exposure to sunlight (think car shows). It would need to be pulled apart and another patch welded in using a butt weld, unless what is there could be saved by cutting off the excess metal (flange). Then, planish and grind down the welds to get the weld seam as close to panel thickness as you can, for the best possibility of eliminating differing expansion/contraction rates and thus eliminating a return of the ghost line.
Looking at your weld picture above, I think the other part of your blowout situation is the wider gaps in some areas. The tighter you get those gaps, the better. Also explained in the tips thread.
