I once saw a Suburban hauling what had to be a 40' piece of steel. They had it slung under it. It was tied off to the hitch in back and the front tow hooks in the front. It must have stuck out 10' in the front and 10' more in the back.
That would have been interesting on the approach to a steep driveway !
Lesser evil..... given the way many people tie-off things on roof racks, I'd sooner be sharing a road with somebody with the steel under the truck, than up top.....