This is a Remix of the Ducato Cupholder from 63bergkvist. It's designed to mount a common car cupholder that's sold in many workshop and car accessories stroes. As well sold in the far east internet stores. I got mine from Biltema in Sweden.
I added the stepfile as well to allow you modifying the part in case the holes or the size in general doesn't fit your needs.

For the fixation of the cupholder i used for M5x12 screws secured with nuts.