I believe in overkill when towing on my car hauler. I use crossed straps with protected loops on rear axle and front A arms. Then a second set of straight straps with T hooks to the factory frame slots to control sprung mass. I have never had a strap loosen during transport with this arrangement, but also could have two straps fail and still be secure. I know its overkill but just like when we tow four down, I don't want issues when travelling. As far as tie downs go, look at Mac's Tie Downs. Also read some of their articles, lots of good info and stories for thought......
Mac's Tie Downs