Actual trade-in will be substantially less than low-retail. Probably about 60% of average retail, but you need to be looking at the real NADA book, the fee version rather than the online freebie. The online version is just estimated depreciation from MSRP and does not take market factors into account. And the fee version will show trade-in values as well as retail. Your local Library may have a copy, but it isn't hugely expensive to buy your own and its handy if you are shopping. One edition of the RV guide is $69.
NADA Recreation Vehicle Appraisal Guide | RV Value Guidebook
Note that the dealer will quote a much higher trade-in value in most cases, but that will include a substantial discount off the MSRP of a new one, or a modest discount if a used one. However, you could have obtained the same discount without a trade, so it's just a fiction to make you happy. If you want to see what they are really offering for your trade, negotiate a no-trade price first and then ask about a trading yours in. Then you can see what it is really worth. I suggest you be sitting down when you learn that. And have the smelling salts handy as well.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL