I would give the same advice with one caveat. The value of any vehicle will vary from location to location, and even from person to person or from week to week. Any item is only worth what someone else is willing to pay regardless of what the book says.
That being said, however, NADA book values are usually helpful in determining relative
values of vehicles. Since the OP has made an assumption of the value of his old motorhome, the NADA Guide should provide a relative value of the Tiffin.