I've had good luck with that method on the floor pans and other accessible areas too. The u!
Ultimate challenge is the upside down seam with a little bit larger than perfect gap. Talk about ugly! Fortunately it is a hard to see as it is to weld.

While we are all sharing secrets, what settings does everybody use for the above techniques? Settings for the thicker plate, the sheet metal, or something in between?

I've tried all with varying success using slightly different techniques for each. Just curious what people's preferences are.