The Navigator is an excellent coach. Just about everything is standard, so if you are using NADA as a guide, don't add for anything, and use the "wholesale" or "trade-in" value as an indication of actual market value. Those figures are available in the printed version of the guide available at banks or libraries. But, a better indication of value is to go to PPL's web site and look at sold Navigators and Monaco Signatures.
In any event, you'll probably learn a lot of useful information talking to an owner of a coach rather than a salesman. So, take the drive.