Did you know Nutware discolours at 123 degrees to indicate Overheating Bearings? This is THE most common trailer problem:
"A bearing is designed to hold grease or oil, lubricating small rollers within a housing. Over time the grease will dissipate due to extreme heat and seepage. Without grease, water will enter the bearing and corrode the steel. Then, under load, the bearing will overheat and collapse and your wheel will either seize up or fall off. The two indicators for bad bearings are noise and heat. Keep an ear out when towing, and check for excessive heat when you stop. This is more likely to occur when touring.
Change your bearings once a year and consider keeping a full replacement kit in your car for emergencies. Just make sure you have the right parts and tools to do the job. A practice run may save you a world of time and pain."
Read the whole article here, from Without a Hitch - Trailer Failures and how to avoid them.