3/8" chain and ratcheting chain binders at all four corners is my go-to setup. Never had anything get loose. Those ratcheting chain binders are easy to use and put a real stretch on the chain! Harbor Freight is a good place to get 3/8" chain, especially when it goes on coupon or when you have a 20% off coupon. But they only have 3/8" in grade 43 (if that is legal in your state). I prefer Truck and Tow for my chain needs. However, it is best to catch their "free shipping" offer that happens about once a month and lasts a week. They pretty much have everything you could think of.
Tie Down Transport Chain | Truck n Tow.com In the photo below, I have since added a fifth chain to the center rear to make sure there is absolutely no movement when braking. <img src="http://www.tractorbynet.com/forums/attachment.php?attachmentid=477659"/>