RV's are NOT manufactured anything even close to the construction of a house. There is no such thing as a vapor barrier.
You have the outer skin, studs (wood or aluminum) and the voids filled with either Styrofoam board or fiberglass rolled insulation. On the inside, you have some type of paneling and that's it.
That's why is so very, very important to ensure there are absolutely no leaks in the roof, why so much attention is given to ensuring correct calking is used and maintained on the roof of the camper. Any minor water intrusion will come from the roof. If the roof is properly sealed and maintained, then water cannot get inside the walls, drip down, across and under the flooring tile and carpet and rot everything out. Protect the roof and the rest of the camper is solid, regardless of how the walls are assembled or what material they are made of.
Again, to answer your question: "No." Vapor barriers are used in houses, not RV's.
Go to YouTube.com and put a search in for RV manufacturing tours, and watch hundreds of videos put out "there" by different RV manufacturers and you'll see what's going on and how these expensive beasts are put together. You'll understand a lot this way.
2019 Montana High Country 375FL
2014 Chevy Duramax HD 6.6 - 3500 Diesel Dully Long bed Crew Cab