I've been lectured over and over about putting four chains and binders on four corners or I will be in "huge trouble". I looked it up in DOT law. As long as your cargo is over 10,000#, this is true. Under that, one at each end is fine so long as there is little chance of side-to-side movement. On tractors, I also use a heavy GR70 clevis on the drawbar to run the chain through in the back. This is also subject of scruitiny as some say to run through the hitch frame or axles. I've never had an issue with DOT or my safety here. I figure if the GR70 chain, binder, and clevis go, or if the drawbar (in good shape)and hitch break, I've got bigger issues to worry about (such as whatever shock would cause that to break). I'd think the trailer tie down rails would be the weak point. I haven't looked this up though. Anyone care to enlighten me?