I designed a magnetic mount for the ICOM 7100
You can download the blueprints and instructions on how to build here: Icom 7100 RAM Magnetic Mount by Angelworks | Download free STL model | Printables.com
It's based on my design for the no magnet version - which I've used all last summer without any issues - hopefully the magnetic version works as well :).
Edit you can get the no magnet version on the same link - in the description tab.