Approx how many miles do you get on a set of bearings?

oldwizard, my mechanic said this was unusual, too, and he is a very experienced trailer guy. I have to chalk it up to rough conditions, I guess. The wheels are 14 inch -- as big as I have room for -- and I am running Goodyear Endurance, fully inflated.

But the trailer bounces a lot on very rough freeways -- no way to prevent it -- and that is going to lead to "shock loading" of the bearings.