When I am towing heavy loads, there is another consideration. How much of my load do I want coming through the back window/cab of my truck when I t-bone the idiot who just ran a red light? Just remember that a body in motion wants to stay in motion and "you" are in the line of fire with anything you are hauling.
In motorcycle terms we used to ask people about the cost of their their helmets, what ratings they had, and then ask them what their head was worth? I think the same principal applies here. It may cost more to secure it properly, but there is peace of mind when you are driving on the road with people that have no concept of braking distances.
I almost always have additional straps or chains because too many times I have come to a stop only to see one of my straps that I just secured a few minutes ago, flapping in the breeze. Everything moves and flexes when you are towing, you just don't see it.