Sources for RV repair information

I was looking for a RV service center with a good reputation and I used Yelp.com to learn of 4 terrible places in my local area and one exceptionally good service center. Normally I use Yelp.com to locate places at which to eat while traveling but in this situation it was a quite valuable resource to find a RV service center.

Does anyone have other resources they use to check out RV service centers in advance?