We just did this with our 2011 Dodge 3500 and 2014 Bayhill FW. Traded them for a 2016 Tiffin Allegro 36 LA with a build date of 18 May. The way our dealer did it was for the FW it was a trade in value (little better than wholesale based on our research). Still gave us more than we paid for it (that was before they new how much we still owed). As for the truck, they got bids from local St Louis dealers and we got way above what we expected. It was close to what I would have gotten in a private sale. Only $14K less than we paid for it in 2010. Not including our trades, we still got about 24-25% off MSRP (not too bad for a Tiffin) and got to order it the exact way we wanted it.
Our main reason we wanted to do this was getting tired of Truck/FW setup. Both of us have bad backs and I have other disabilities from 20 years in the Air Force so going to a Class A was the best option for us as we love RVing.