I needed a solution to the weak rear rack so I can mount a topbox with confidence. Having somewhere to store tools, a flask, or even two some sandwhiches while wandering around is just so handy.
The rack is not really designed for much load and it tends to break, as in this attached pic (from the web)
They tend to break at the same point where this a high cantilever load on a piece of bent pipe.
This solution shows extra supports clipped to the rear of the rack and to the frame. as shown here.
The extra supports would need to be slightly bent and may interfere with subsequent fitting of pannier racks.
(Although I noticed that Norally (Itchyboots) does not have side racks an Dhanno)
This solution involves welding.
It moves the stress point away from the weak area to the other side of the rear supports.
I think the breaks have occurred due to metal fatigue as the rack flexes slightly up and down, If you thump the rack you can feel it vibrating at a high frequency. The tubing used on the rack is 16mm, but measures a bit thicker probably due to the paint.
I decided to add some tubes following the line of where the bottom weld is in the picture above. This transfers some of the load to the other side of the rear support and should stop the rack flexing at the usual break point.
I have no welding equipment so it had to be nuts and bolts. The clamps are pipe clamps. They are stainless steel and come with a rubber lining. I was happy with the lining on the box mounts but I wanted a metal to metal joint for the reinforcement. The clamps are sized with the rubber lining. So 16mm size with the rubber was fine for mounting the box but I had to go right down to 10mm for the reinforcement.
The above is my solution.
Update 18/6/2020
I have removed the small box and fitted my old Givi box. This will hold lots of shopping or two fullface helmets. I would not have been happy to do this with the un reinforced rack.