Every fall new wheel seals, remove bearings, clean hubs, inspect pads and calipers for any seal problems, repack bearings and reassemble with fresh grease, bleed brakes 1/2 pint min. Wheels torqued to 85-95 lbs and tires to 65lbs or max pressure as indicated on tire. I also try to wash & wax the trailer.
In the spring before the Dale Hollow trip check springs, tire pressure, recheck wheel torque and 2 pumps of grease per wheel into hub. New tires every 7 years weather they look bad or not. Of course light check every time the trailer is hooked up, Every 3 weeks wheel torque check and 2 pumps of grease per wheel and tire pressure check. Since I ski in a muddy river I go to the car wash once a month and get the dirt off the trailer. I always wait a min of 10 minutes before I launch the boat after trailering to allow the hubs to cool down some.
Maybe overkill but it works for me.