Many plugs corrode internally - under the plastic / rubber, you won't see it until you cut it open - with all the towing you do I would do a couple of things, I'd get a trailer wire maintenance kit - it comes with pin cleaners, wire brush, files, grease, cotton swabs and instructions, a few companies make them - some better quality than others but at least you'll have the proper tools to do the job, each piece can be replaced with better quality if / when needed - I'd also replace the harness with an all-weather one, the all weather are blue, not only are they sealed better they don't stiffen in cold weather a major plus for snow users!! You also want to make sure the trailer battery is in good shape - the battery can cause issues with the system, even when you thing the truck power is taking over. A simple trailer plug tester will let you know if your getting the proper power to the trailer another nice item to have - sounds like a lot but like worth not having to test the pucker power....