To the OP, does the reflective strip on the rear of your rack trunk have an unsewn section in the middle of it for sliding a light onto it? Besides mounting on the rear of the rack in place of the reflector, which is a good idea, I have put a cateye light that has the clip on it on an ankle/pant strap on my left ankle with the light facing backwards, so when I pedal it is moving up and down. They used to make bike lights of this sort that went on the ankle. The movement catches the attention of drivers.