Well while I'm having my first cup of coffee for the day-------and I did mention earlier about air loads from passing semi trucks--------on an open trailer, don't forget( and I know that from your aircraft work) about the drag from the air around the car at speed-The tiedowns will have to hold the car against that load also.

Just yesterday I was over at a premium level type collector car place and a guy brought in a late model Corvette --------He had a Caddy Escalaid? for a tow vehicle, a box trailer (more like maybe a landscaper/carpender than a vehicle trailer) wood floors, horrible conglomeration of a ramp door-----Front of Caddie up about 10 inches, rear squashed down til the hitch almost drug the ground (even after unloading-probably had 1000 lbs stuff in nose of box) and brakes only on one axle but no apparent wiring or surge system to operate them

And I won't even get started ( until after 2 or 3rd cup) about the guys who'll load a car backwards.