I cut up a strip of old tire tubing and wrapped it tightly around one of the rear rack posts until it was thick enough for the standard blinkie mounting hardware, zip-tied the tubing so it didn't unfold, and then mounted the blinkie vertically. Haven't had a drop of trouble with it. It should be noted that I never tried to mount it horizontally, because I thought with the weight and all the bouncing the light might "wiggle" out of place and start facing downward....but vertically mounted, it's cake!