I haven't seen any replies yet, surprisingly. I had one installed on my former Model S five or six years ago by the Watertown Service Center, before Tesla had policies prohibiting working with non-Tesla accessories. The Model X that replaced it came with a tow hitch. But there must be others around here who have had Ecohitches installed since...
You might try Wheel Dynamix in Natick - Jeff does great paint protection film and tint work on Teslas, and may do more involved things. Or Hollis Autobody in Ashland or Today's Collision in Malden, the two local Tesla-certified body shops.
Please post here if you are successful - I might be interested in getting one on my Model 3, for use with a bike rack.