This photo shows the rusted piece being replaced ... still attached by a few stray threads.
Testing fitting the patch
Tacked in place with the left seam done and the Cleco holes welded up.
Bottom seam done all the way across. Still a lot of work to do, lot of pin holes to weld up, lots of other small sections to replace. Upper seam will be a bit more difficult because it's harder to reach with the various grinding tools. Good technique for doing any similar area like rockers etc. Used a Lincoln with .025 Harris wire, CO2/Argon mix. Was tempted to use TIG and silicon/bronze but too much contamination from dirty back side on the metal.