You're trying to transport two different types of loads. Personally, I prefer the wheel straps for transporting cars and trucks (assuming they fit the tires on the vehicle). Versus tying down to the frame of the vehicle. The reason is, tying to the frame sucks the cars suspension down or, allows the vehicle to float as you hit bumps in the road. That floating can cause straps/tie downs to come loose. Using the tire straps secures the vehicle to the trailer and still allows the car to ride on it's own suspension and the trailers. At worst case, use the control arms if you aren't going to use the tire straps. The tire straps are not going to work on the rear tractor tires and most likely won't work for the front.
For the tractor, use straps or chains attached to the appropriate trailer tie downs and to the tractor using secure points already on the front and rear.
Personally, on my own tractor, I attached a receiver hitch to the front onto the frame. That allows me to move bumper pull trailers around with ease and provides a tie down point for when I need one. It's also handy for when (and you know this is going to happen) you get stuck. You'll now have a tow point in both the front and the rear. Just my 2 cents worth, do what you will with it.
Rams :drink: