Welcome to the forum....
RV's manufacturers assemble the units primarily from stock parts that are available from many component manufactuers. If you are interested in a motorized RV (for example, Class A, Class C or Class B), you are actually buying a motorized chasis and a "house". Many of the chasis on the market are manufactured by a separate firm that makes just the chasis (engine, transmission, and the frame on which the motorhome is eventually built) and the RV manufactuer then adds the end caps (on a Class A) and the sidewalls, roof, interior components - seats, cabinets, sink, toilet, shower, roof air units, etc) and just about all of this stuff is available for repair/replacement from OEM sources.
Engines/transmissions are all made by firms that specialize in those components. The only RV firm that I can think of that is curently making their own engines is Navistar (Monaco) who has recently started offering their MaxForce line in some of there new units. Most engines are Cummins or Cat's for diesels (but Cats no longer in the market), or Ford or Chevy for gasoline units.
Allison seems to be one of the most popular transmissions. These components can often be serviced best by the specific manufactuers service network.
Some parts are available from your local auto parts store - particularly for units that are gasoline powered, but when that is NOT the case - like for some of the diesel powered units, the alternative is a truck parts supplier.
Getting repairs is generally not the issue, but the fact that you will need repairs - either do it yourself or pay to get it done - is a certainty and if you plan to pay to get it done, the problem becomes finding someone who is both reliable and affordable - often not such an easy task.
But come on in, the water's great!
How is it one careless match can start a forest fire, but it takes a whole box to start a campfire?
Dan & Linda, 2008 Camelot PDQ, 2008 Jeep Wrangler