One item that I think has been overlooked is the proper height of the hitch in relation to the trailer axles. Depending on what your towing with and if you have an adjustable height on the ball, you could be loading up either the front or rear axle of the trailer. Both can cause sway and overload the trailer tire rating. For example, if you tow with a 4 WD pick up your hitch height is probably going to be higher than 2 WD vehicles. If you don't adjust the ball height to have a level trailer, you will put more weight on one of the trailer axles and therefore tires. You can see this at the spring connection point between the front and rear trailer tires. That pivoting lever that holds the spring ends should be level.