Great pictures please keep them coming.
So I screwed up on my dimensions of the overall width of the box,
I knew the truck frame was 44" wide, after I flipped the box over and of course only after I welded the L support brackets to the box sides
I discovered that I was 2 3/8" overall short of the 44".
I made up inner fenders for the box sides 1 3/16" deep to get back to the 44" overall width to match the frame, but now I would have no access to the nuts that would be required. I tack welded nuts to the inner fenders so I could still run the bolts thru the wood or steel panels.