How are you tieing down your car in your enclosed trailer
1/2 the time I am a lazy, just winch the car on the trailer, wrap a chain around the rear axle, and tighten the winch and go.
Mostly just parts cars, because after fighting them to get them on the trailer, I just want to go home.
I do watch the mirrors like a hawk on the way home, to look for movement, and check all tightness anytime I stop.
I have not lost one yet, once in a while the winch cable will get a little slack. But most hauls are short distance, that I pick up local.