The here are 3 big problems with trailer bearings.
The first is that they last for many years with minimal maintenance. Until they don’t. And they never blow up when the boat is sitting still, in a well-lit garage, that happens to be full of tools and cold beer. Plan accordingly.
Secondly, there isn’t any comparison between boat trailers and utility/box trailers because nobody backs their Harley Hauler trailer into the water until the hubs are completely submerged in muddy, gritty lake/river water.
There is no such thing as a perfect rotating seal, so just because the seals appear not to leak any grease, that doesn’t mean that moisture just from condensation doesn’t form in the hub even if it is sealed from the outside moisture. Therefore, there can be corrosion forming on bearings even if the seals are still good.
I do a postmortem using a parts washer to clean every trailer bearing and race that I change (and I do quite a few) and 100% of the bearings I change have some form of foreign material damage or they have signs of pitting/corrosion or they have all of the above. This isn’t to say failure was imminent, but the bottom line is there is no perfectly sealed bearing.
Third, there is the problem that you can’t inspect trailer bearings properly without a complete teardown including removal of the races, and then running everything through a parts washer, then inspecting. So obviously the only course of action that really makes sense is to replace bearings at intervals because inspection is the same amount of work as replacement.
Now the “be prepared for a roadside bearing change” theory with spare hubs, grease, tools, etc is a good idea, but that only works if you don’t clustermuck your axle when your neglected bearings do a meltdown on the freeway at Mach Jesus. Again, I inspect axles on every trailer I do, and if the bearings have at some point failed or are badly neglected, there is ALWAYS axle surface damage. Most of the time it can be resurfaced out, but remember that failure is always a bad option because you aren’t carrying a spare axle.
Bottom line with Midwest boat trailers is to run good bearings, good grease, and Bearing Buddies and then replace your bearings every 5 years regardless of mileage.
