They sit on something on the bottom and behind something on the top, like a shelf with eating utensils, the cabin light, the instrument shelf, the throttle levers, whatever. They are very utilitarian and flexible. I have two differnt sizes, like I use in my truck when I leave it parked. One size fits the front, and one size fits the side. They are not expensive, get a single pair and try them out. If you don't like them in the boat, they will work in the car. I also use(d) them for reflectors in my photography.
Harvey
SleepyC :moon