A rotating stand for a TRX-4 RC car, but with the 'Chassis Tray' part on top it should work for a range of models.

3/8" balls for the bearing, although a range around there should work fine (sorry, I'm lazy or I'd actually calculate what that range is...the step file is there...you do the trig :) )

On the 'tray', I added adhesive-backed foam strip to just pamper that undercarriage.

I really like printing the base in TPU. It makes it really 'plant' well to the table, and also makes the bearing much quieter. But the downside is that the bearing doesn't spin nearly so free.