Backtrack on drilling out spot welds. I chose to buy groups of 10 drill bits at Harbor Freight when I was removing panels. Drill out 10 or 15 welds, throw out the bit.
Problem is that leaves a bunch of holes in the remaining metal. This is the view of the bottom of the inner rocker with the holes, you can see the intermediate above it.
Enter the copper backer...it lets you use the welder to fill the holes but the weld won't stick to the copper.