Surface mount for TechMatte magnetic phone mount

I recently bought a TechMatte magnetic vent mounted phone holder (https://www.amazon.com/gp/product/B019GL78NK/ref=od_aui_detailpages00?ie=UTF8&psc=1). It works well, but I wasn't crazy about the vent mount part.

I designed this piece to re-use the magnetic part of the mount, but allow me to mount it to a flat part of my dashboard with two sided tape. The magnetic part of the mount fits over the ball perfectly, even with a coat of primer and two coats of paint on it.

I also designed this p