No less then 10,000lb straps. Depending on what you have for anchor points on the trailer and car. And you want to crisscross them front and back if possible.
I have brackets welded to the rear housing that I can just clip my hook onto and tighten from there. On the front of my car I use the "tie back" version and also keep my winch cable tight. It will probably take you a few times adjusting the cars weight, etc. before you get it right.