Actually it's holding very good in my opinion. I made 3 trips till now. About 600km on each trip, with the E22s fully loaded ( one fully loaded E22 with clothing, towels and similar stuff is about 5kg each). Also made about 1200 km without cases, so about 3000 km in total and not a problem.
For the Fehling brackets, the only source I found at the time I was researching was http://www.fehling.de/index.php?content=preise&markenid=10&lang=eng
. But I don't like how they are attached on the "pillion handle bars" and also the price is a little to high for a product I don't like 100%. In the 2014 there was also this guy from https://www.youtube.com/watch?v=JMCNXjbl_PQ
that I contacted, and he had the brackets (in black only, there were 99€ plus 13€ shipping), but I didn't buy them at the time. By 2015 he was not returning my emails anymore.