Originally Posted by Rowan

It's one of the easiest conversions you can do. A knife to cut off the backpack straps, a screwdriver, an adjustable wrench, some tonneau tiedown hooks that should snapfit over the rails of your rack, and some nuts, washers and bolts. Measure and screw together. I did four from old canvas backpacks handed out during a special event in my home state. They needed straps to wrap around the racks and the panniers to keep the bottoms in place.

If I were to do it again, I would use commercial clips available from, say, Ortleib, or make my own similar to Arkel.