So, finally I decided to go with the original Royal Enfield Aluminium Boxes.
I ordered them right in India, and they arrived amazingly fast and without damage.
Painting of the racks looked good, boxes are in reasonable quality.
Mounting of the racket was a nightmare, since the connection points did not fit. Obviously the rack was misaligned due to welding without a proper fixture.
I finally managed it. Once everything is mounted properly, the whole stuff ist very stable and solid.
Regards
Toni