I had a friend have a sled come off of an open trailer on the Macinaw bridge while going up to the UP. The sled slid along and never flipped because they were going slow. He hopped out, ran back to the sled, fired it up and drove it back on the trailer with the cover still on!! Must have been a good show for the other drivers.
Do what I do....use a chain to secure them at night and while trailering them. A sled coming off trailer can kill somebody. Or worse , a bus load dodging it, over the mountain!!!!