Thanks to some helpful criticism and some even more helpful "how to", all 4 corners are welded up solid.
The first picture is of the first corner I did. There were some "holes" in my weld. So I touched it up.
IMG_1923 by
Robert Moorman, on Flickr
I know there looks to be a pinhole, but that is the first pass under the second pass. I have not worked it with the flap disc yet.
Then on to the 4th corner.
IMG_1925 by
Robert Moorman, on Flickr
The inner support, with the primer runs on it was still primed except where the welds are. The primer was up inside everything.
Then welded in place.
IMG_1926 by
Robert Moorman, on Flickr
I had some blow outs, still trying to figure those out, and I had to re-weld and re-grind 3 times in some places to make sure there were no pinholes. I think it's solid. It looks correct and it will take only a skim coat of filler to make it ready to paint.
Now on to other parts. I got the mounting plate for the side vent welded in, but still trying to figure out how to mount the vent on the plate. There is not much room in there.