Hmmm.... that pic may not accurately show the frame centered on the tubes, but at first glance it looks like the inside rails are closer together than the center to center measurement between the tubes. If so, that's wasted space. And I have never understood why anyone would run a double rail without decks, whether diamond plate or HDPE or plywood - once you run decks, you'll never run without.
Gary made a frame for a 'pard here in SLC, we built the floor (HDPE), hatch covers and decks (aluminum diamond plate) and it came out really nice. Whether disbelieving or for whatever reason, Gary cut the cross pieces too short, but made good when provided email trail of measurements. The fittings are great. The oar tower setup does get your oarlocks out another 3-4 inches from the outer rail, those concerned with banging into walls/rocks will want to keep them inside the outside measurement of width of boat.
Nice workmanship, just hard to tell from the pic if the inside rails are correctly positioned...