Take a lok at the attached link below an you can see why your 'old' RV has depreciated so much. With over a half million new units delivered in 2017, there is a glut of used on the market. If you were buying used, you can deal. New with a trade - good luck as it is not a good owners sell market. Looking at NADA will not give you anything honest in an RV as their numbers are based on something pretty fuzzy. We would love to buy a new unit but wont simply because the loss would not be nice - and we have never owed a penny on the purchase.
Read and weep:
http://www.rvia.org/?ESID=histglance