I recently got an RTL515. I've been loving it so far, but it mystifies me that Garmin didn't provide any sanctioned way to mount it to a seatstay. I have a collection of about ten vintage bikes (nothing newer than early 80s), so all my top tubes are level and I ride with either a saddle bag or spare tubular tire under the saddle. Mounting to a seatpost is simply not an option.
For the moment, I'm using the aero seatpost adapter mounted upside down on a seatstay to provide a way to mount the device in a more-or-less level fashion. My biggest concern is that the contact surface between the seatstay and adapter is minimal, which allows the Varia to rotate. I'm also a bit worried that the o-ring isn't as snug as it would be when used on a seatpost (rotation and involuntary unmount when hittinig a bump).
Is there no optional mount for seatstays? Anything from a third party? I checked the Thingiverse but saw nothing there for seat stay mounting.
