I you have a panel like that rocker that is getting totally replaced, sometimes is makes life easier to use a cut off wheel and remove all the excess not welded. ie: cut up to the spot welded flange as close as possible without damaging any adjacent panels. The intent is to get rid of the bulk of the panel and leave just a strip with the spot welds, then as you begin removing spot welds you can roll up the strip with a pair of pliers as you go. In some cases this will make it easier to find spot welds that are hard to see.
Here's what I use in removing the spot welds...
http://s5.photobucket.com/user/rmcc...n%20Album%203/RemovingSpotWelds.mp4.html This process gets used when the top panel facing you is the throwaway. I like using this primarily because it is easier for me to not cut too far. I've had too many instances where the adjacent panel required repair from using a holesaw type spot weld cutter that obscures the view of how far along you are, even cutting all the way through in some cases. But if the bottom panel is the throwaway and you're saving the top, just drill through the spot welds and the hole will serve as your plug weld hole when the new panel is in place.