I've found that by checking with GM (I'm on a Chevy van body) for commercial vehicle dealers usually result in having a facility with the equipment to handle light and medium duty trucks. If they can work on a box van, they can work on an RV. I also found that size (as in length) is another factor as getting service for 21 footer isn't that hard compared to a vehicle needing a longer lift or bay.
What has become an issue isn't finding a facility capable of service an RV, but finding a facility willing to do the service you need done. Seems many RV dealers and service centers are no longer interested in diagnosing and repairing issues and want to just replace with new items.
