Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2747846.
UPDATE: Added version 2 stl file. The 1st version failed South Carolina's May heat. The metal ball popped out when I pulled on the base. Version 2 has a much firmer fit.
I already had a ProClip Angled Dash Mount installed in my car from a few phones ago. Instead of buying another one-off mount for my current phone I decided to try a Universal Magnetic Car Mount and stuck it to the ProClip base with the included double sided foam tape. Well the tape didn't last a month in the hot weather here in the Southeastern US (and it was October). So to fix it I got out the digital calipers designed something in Tinkercad and printed it on my new 3D printer. What I came up with is a custom base for the steel ball of the magnetic mount to snap fit into with holes to mount the whole thing to the ProClip base on my dash. This thing is working great so far. I'm hopeful that the solid printed PETG will stand up to the heat this summer. Fingers X'd.