Like many others here I found that sewing/zip tying the mount to the back of my seat pack was a simple, light and elegant solution.
However, I've become attached to my Silca seat wrap style pack which does not offer a secure mounting position. Resorting to the round seat mount is a not great option for me because the bike is a Trek Emonda which has a seat mast with a large diameter (35mm). The rubber band mount is just too sketchy for me, and is really intended for a smaller diameter anyway- the bands provided are clearly stretched beyond their designed length.
The rubber band mount works fine below the level of the mast cap, but this places the radar (and light) very low on the post.
Garmin sells a hard plastic round seat mount which is far more secure but again this is intended for diameter smaller than 35mm.
I found that a short velcro strap (6") threaded through the rubber band round mount provides a very secure mount on the mast cap, allowing a relatively high mounting position, given that the Silca wrap sits very closely to the saddle.
Very simple, very light, very secure.
