Much of getting repair work done is a matter of networking. talk to people. Ask around with friends / coworkers / neighbors / church group -- whatever..... Someone always knows someone who does that kind of work. You don't need an "RV engine" serviced, you need whichever model of engine used in that chassis serviced....and when you discuss it further you can tell them it's in an RV. This applies farther than just the main chassis - I don't know the specifics of your RV, but I do know the same engine powers certain RV generators as what powers some little Kubota tractors I've dealt with - belts, filters and so on -- all the same.
If you are mechanically inclined, then basic maintenance stuff is very much like any car. If you can change the oil in your car / pickup truck, then you can change the oil in your Freightliner chassis'ed RV - there's just gonna be more oil (bigger drain pan) and possibly more than one filter.