Honestly, since Grand Design doesn't even book in NADA yet, you would probably get somewhere between 70- 80% of what you paid retail.
Take into account that it is now a used coach, with no warranty, and the dealer has to sell it as such.
It will really all depend on how the dealer shows you value. If the start at MSRP, you may get more than what you paid for it, the money just shifts from one spot to the other...