I posted this in the trailer/towing forum.
Tire pressures are a random guesstimate. The tire manufacturer and truck/car/boat trailer OEM's are also a guesstimate. None of them have any idea on what load you are actually applying or weather conditions (hot/cold) you are going to be running at. Full load of fuel and gear also makes a big difference. The only accurate way to determine the best pressure throughout the year is to chalk test the tires. I've done this for many years for my vehicles/trailer and established outdoor temperature guidelines as to when I adjust the pressure. This process gives you maximum longevity/performance of your tires. I found an excellent video showing the process: