Mike came over and welded up the seat tubing so that's done
Also made some small flat support plates in the center floor area in the interior. Used .100" chromoly sheet, then cut and bent them up to make them flush with the top plane of the lower tube.
With the 1 5/8" outer tubes and 1" cross tubes there was about a 3/8" drop in the middle. With the pads done, the aluminum floor will now be supported and have no droop.