I'll be using plug welding for a lot of this, replicating the factory spot welds. I have to say, it's harder than it looks...I did a bunch of testing on scrap and did some research. A larger hole helps, like 3/8, and you really need to focus on getting the arc going on the piece behind.
If not, you'll get a really nice looking plug weld with the hole filled but no real penetration to the piece behind. Some of my early tests...some held and some did not.