This is a 42 mm cap, a replacement for OEM part 1K0092702O (the last two images). I made it for my T6.1 Multivan, worked for a friend's T6 Caravelle too. Fits all VAG vehicles with towbar like the one attached as an image. AFAIK those are Volkswagen T5, T6, T6.1 (Multivan, Caravelle, Transporter, California ... they are all the same). As I searched through the Internet, I found some places that claim this fits some Touran and Westfallia models, please comment if you can confirm or reject this info.

I borrowed the design from the 41mm OEM design of 1KM092702W. Although visually similar, this model will NOT work for the 41mm tow bars.

Fusion 360 model is at https://a360.co/474t15k (could be newer than what is uploaded here)

Designed with 2.4mm wall size, so that nozzles 0.2, 0.3, 0.4mm, 0.6mm, and 0.8mm would work just fine. No supports needed, as the slicer would usually slice the overhangs as straight lines and there are plenty of layers above to fix sagging bridges. I've printed it with PETG but it would be even better to use something a little bit more flexible (e.g. the 68D shore hardness Bambu TPU for AMS or something stiffer than that)