I've tow a lot of different cars on open trailers, car hauler trucks and enclosed race trailers. I used to use only two tie downs until we wrecked and totaled 1969 Hemi GTX on a borrow open trailer with one tie down on the front and rear. The rear tie down (dog chain size tie down ) chain broke when I slammed the brakes on my pickup very hard after hitting a dog that ran out in front of my 1/2 ton pickup truck, the car ran up and over the front tire stops and onto the back of my pickup and then flip over onto its roof totaling it
I now use 4 5000 Lb. rated ratchet tie downs, one on each corner, and make them tight as I can get them, if I'm going more than 30 miles I try to stop after 50 miles or more and retighten the rear ones around the rear axle to remove any slack in them from rocking, normally one to two more clicks and then they stay tight no matter if I tow it another 100 to 800 miles
I leave it in neutral and i back off the winch line to get slack on the cable, so I don't trip on it when I go in to untie the tie downs to unload the car I use to leave the winch line tight until I wore out one winch from the rocking the gears in it when stopping and starting forward again in traffic. That tore up the gears in that winch , No more problems since loosening them up a little