I cut out the rust on the floor and rear cab wall of a 1980 Toyota Pickup. Then I welded in a section of nice floor from a donor truck. Next, I fabricated a patch panel from a piece of scrap sheet metal. Finally, I welded it in, then primed and sealed it. Full length tutorial: https://youtu.be/QhTj69FLvuA
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Amazing seeing the whole process come together.