I have the same trailer that I just bought in October, so a lot fewer miles, but I have not heard anything about the bushings. I don't recall reading anything in about that in the owners manual either.
I would hope that the trailer would be designed to get more than just a few thousand miles out of these bushings though. But what do I know, I'm pretty new to all this.
Sorry I'm not much help with an answer, but I'm very interested in what you find out.
2011 Chevy Silverado Crew Cab 4X4
2009 210 WBS