Many buyers are reluctant to purchase privately because they feel they need a dealer's facility to service the unfamiliar and complex systems in an RV. Financing is also a mystery that many do not wish to deal with on their own (but it is really easy if you work with any of the several companies that specialize in Rv financing). The net result of that is that you usually have to attract buyers with ultra-low prices. A few people have managed to get a near-NADA book price in a short time, but often private sellers find it can take 6-18 months to get a buyer at even a steeply discounted price. I'd suggest setting a price modestly below NADA book and advertising for awhile and see what happens. If the right buyer comes along, you can sell. If not, just keep the rig.
You might wish to locate sources of RV financing to assist would-be buyers. An online search for "RV finance" or "RV financing" should turn up several and you can give buyers phone numbers, web site addresses and maybe even application forms. Some companies are Ganis Credit, Esses Credit, and Beacon Credit. These are all reputable companies who know how to handle private sales.