Before I put this piece of metal in here, I took a putty knife and separated the floor pan from the rocker flange, only about 1/4" deep. That way when I weld in my new piece, the weld will be underneath the rocker flange lip and you won't see the weld. The copper strips I put in here are .025" thick and I will weld it solid on the back side where you can't see it. In this picture you can see where I welded above the copper strips on the outside.
I used a dremel wheel to grind down in behind the flange of the rocker to cover up the weld, then I will draw it tight and plug weld it. When I'm done, I will have a nice definite edge on the rocker panel flange.
Here's a roughed-in picture, the lighting makes it look bad because if you look at it in normal light, it has a nice definite edge. I didn't finish it up because I wanted to get the pictures online.
I stuck the floor support back in and then went around to the back side to take a look at how the pan is sitting on the support, and it looks like it will be tight. I guess the gist of it is you can hide weld with copper strips. After looking at these pictures, all of this work doesn't look very good but I think it's the light I had on it because it really did come out nice.