Mark, I just towed a small motorcycle trailer that I converted to a double Jet Ski trailer 1200 miles and had ZERO problems. My average speed was 70 mph and hit 80 for awhile.
My 5.30x12 "C" load rated tires are rated at 1045 lbs each at 80 PSI. I weighed my trailer and it was 850 on one side and 800 on the other. I kept the tires at 80 psi and checked temps of tires and bearings religously with a digital gage and tire temps never went over about 115 degrees and bearing temps never went over 95 degrees and it was 88 degrees outside the one day.
I did install new wheel bearings and pressurized grease cups prior to the trip (about $40 total).
Check the condition and load rating of the tires vs the weight of the boat/trailer and if well within limits, maybe pull the wheels and inspect or install new bearings packed with marine wheel bearing grease and you should be fine. Make sure you have a good inflated spare and tools to change.
