I used the Garmin mount that generally attaches with their heavy duty rubber bands. I sawed a slit in it that slides over the flat bar at the back end of my rack where you'd normally attach a light or flasher. Instead of the rubber bands I wired it on since the bands would not tighten it sufficiently. If need be, I can try taking a photo of the setup tomorrow.
That would be awesome to see
Here's some pictures. I used a hack saw to cut into the mount from the bottom, creating a narrow slit that slides over that flat cross bar. But you can improvise to wire or attach it or do as Volt suggests.
I use the same bracket for a Varia RVR315 but in it's normal attachment on the seat rail. It tucks in securely and unobtrusively under the seat.
Although, there are reviews that the Go-Pro adapter on which the Varia is mounted is "plastic" and has broken. But in their pictures, that part is a white plastic (plastic or some form of nylon stuff)
mine was all metal. maybe they changed it. this one is morel ike mine https://www.amazon.com/dp/B0832D9DM...9Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=
