On our last trailer, we had several wheel hub failures (not fun!) so we have been perhaps overcautious with the newer TT, which is smaller and lighter (I suspect we did overload the previous TT, which exacerbated the problem). We found a great mobile mechanic one time when we were heading out on a trip and noticed one wheel was leaking grease (oh no, not again!) so we went back to him - 80 miles away from our home - a few more times, every 5000 miles or less. He got another job and wasn't able to do it anymore, so he recommended we go to a reputable chain (Les Schwab in this case) which specializes in wheels, tires, brakes, etc., as they guarantee their work, and can be found in multiple locations, should we have a problem on a trip. We now take it to them once or twice a season, depending on our mileage, for bearing service. The mobile guy, the last time he did them, put in Japanese bearings, because he said they were much better than the cheap Chinese ones. Anyway, they have not changed the bearings for a couple years now - they have inspected & repacked them, but they keep telling us the bearings themselves look good. So it seems to me that good routine maintenance, and using good bearings to begin with, may indeed mean that bearings can last a long time.
