I took two aluminium stripes and drilled the holes for the fans. The top two screws und the lowest two screws connect the fans and the stripes directly.
The eight middle screws are screwed through the case (new wholes have to be drilled) so the stripes are fixed to the case and the fans are fixed to the stripes.
Further i had to cut the mounting points for the 120mm fans and cut out a little bit of the case at the bottom.