I have a mix of various hanging trays and needed to connect them to my multiboard. A few holders found online but none fit what i needed as they used other attachment styles than the standard multipoint connectors i already have a ton of. I also wanted to be able to use the multipoint slides as well to allow for finer positionin when required.
The side slide style should be printed on their end standing tall. Either end up should be fine.
The top down variety should be printed standing horizontally.
No supports required for either. I did use some mouse ear brim just to keep them happy and upright though for both.

I recommend lite multipoints because they fit a bit more snug and you are less likely to pull the hanger off the wall when lifting off the tray. This is mitigated some by using the slide model since they are applied from the side.
Lite Multipoints - https://than.gs/m/1123321
Multipoint Rails - https://than.gs/m/1131087
The author marked this model as their own original creation.