Not to be negative, but I would also add some fish plates over the butt welds on the main rails ahead of the rear bags. On a race car butt welded joints need to be reinforced i.e. gussets or fishplate. I know it's not a race application, but I would think bumps and pot holes would be just as hard on a frame or even more so than a race track.
just my 2¢ for what it's worth.