Time for my first how-to share... :-)
After much messing about I have managed to fabricate a pair of soft pannier support bars that fit with only two bolts each. They both bolt into captive nuts for ease, and the mounting bolts live on the bike when the bars are removed. They are rock solid when mounted due to reinforcement with flat bar at the bending/mounting points.
This is what they look like:
I made an inverted "V" bracket that sits permanently behind the number plate. This was made from two bits of angle welded together in the middle of the "V". The angle iron was cut-down to just leave a "lip" - it adds a lot of rigidity for not much weight. I also welded a captive nut at each end for the pannier bars to mount to. Captive nuts make life easy in the future!
Apologies for the welding quality but I only have a stick welder and I am far from professional - more of a grinder than a welder, but I can stick metal together so that it stays together. Good enough for me!
The rear of the support bar mounts to this "V" bracket, and the front to the nut that's already there in the end of the tube behind the passenger footpegs:
Details for the bars themselves.
If you look closely at where the end of the bars are flattened and bent, you can see that the metal looks a bit "messy. This is because I welded a piece of 3mm bent bar on the inside of each bent tube - from the end of the flattened part and up towards the unflattened bar. I then ground it back (quite roughly, but it is hidden when mounted, so bugger it!) and drilled the holes straight through the flattened tube and bar combined. This makes them very strong and is essential imho:
If that's not fully clear I'm more than happy to answer any questions about their construction... :-)