The Polaris racks are a composite plastic, very strong . You can mount just about anything to them just drill a hole and use a backing washer or plate.
I have several different boxes that i made and use for different seasons that i just bolt to the rack.
One for my auger and ice fishing gear , another for moose and deer hunting, and another for just hauling tools and a saw.
Get creative and show use what you come up with.