I used to drive 5 ton, 2.5 ton, hummers and postal vehicles of different sizes out of AM General's factory in South Bend, Indiana and load them onto rail cars all over northern Indiana. We always secured them by the frame to the rail car bed and ratcheted them down to compress the suspension. After loading, a military inspector would come by and inspect the job before the train was allowed to move. I probably did several thousand of these.
But, I have never moved a car on a trailer on a highway. I would have thought that you would not want the car to be able to move at all and want it as solid to the trailer as possible, so that the trailer's suspension would be the only thing moving back there. That would require ratcheting it down to the trailer to compress the suspension.
But after reading the advice of people that have done it, I am torn between the two.
