Depends... are you looking at the retail nada (what a dealer would sell the same unit with the same options), what you would sell the unit to a dealer (trade in), or what you could sell the unit to another private party (or they buy from you). If you are selling to a private party through Craigslist, local advertising etc... look at the Nada low to average retail. Someone trying to buy from you may offer you the low while you may try to sell at the average. You more than likely won't get what a dealer is asking (high retail). And.. are you 'plugging' into NADA all the options that came with your tt?
Something of interest.... pre-Jayco, we owned a 2004 17' Casita. Casita's were hard to get and much sought after (before Jayco made the mini-van towable tt as they have now). The resale value for that lightweight little fiberglass 'egg' was out the roof. Our 2004 Casita with options NADA valued at about $7k in 2009 and sold for $10k in the (non-dealer) resale market. I don't think your Jayco would have that kind of resale value, but make sure you get the NADA value for ALL options purchased on your x17z.... ask "middle book", but don't expect what you paid. Hope this helps