Doug, we had the same issue with the shiny Riv rack on a Wilbury. I asked the fine folks at Rivendell, who suggested we rig something up with stainless band clamps (or P clamps), the Nitto versions of which (
https://www.rivbike.com/products/nitto-band-clamps-pair) have been sold out for a long time, and M5 or M6 bolts and nuts. I found some good stainless clamps at the local hardware store and affixed a taillight plate to the rack with no issues at all. It’s stable, with no shake or quiver.
It’s a great rack, especially for the money, and I wouldn’t hesitate to buy one again. The only shortcoming was the lack of the tail light plate, and it was easily remedied with a couple of dollars for the clamps.
Jim
All,