Heckflosse,
I just finished viewing the Rover website photos. It took awhile to get to them as it required registering and then waiting for confirmation of registration before being allowed to view the posting (Aproximately 15minutes). After viewing all the rust that you had to repair, I am impressed with your fortitude and willingness to save your 111! I just finished having my 220SEb cabriolet stripped and painted and fortunately the only rust was in the left spare tire well (typical for a convertible) and the same cross member rust that you had above the gas tank. No rocker or wheel well rust as it was formerly an Arizona car. Hope the finished product turns out well and look forward to final pics. See my rust in thread and what I did with that area after repair:
1970 280 Sel 108 chassis body work question.
111 Cabriolet strip & new paint