While this is not the best project to learn TIG wleding, here I am trying not to screw things up. I had the sheet metal fabrication house bend the 'tabs' of the bottom up 90 degrees, I left the corner radius's empty. I used a section on metal with rivet holes already in it, formed it to fit the radius, and welded it in place. The result, much to my suprise & delight, was a water tight joint that the rivet holes lined up with.
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