does anyone know what the rubber belt thingy on a dommie rack is for? one of those things that every time i see it, i scratch my chin and then forget about it. i have used it for carrying every thing from fishing poles to wooden battens from the diy shop. also under the rack looks like a mounting system that uses a tube that goes underneath the rack. i'm sure there's a simple explanation, but i still havent heard it. thanks!