If they want to make the sale bad enough you "may" be able to approach something less than a grab your ankles trade in price. Negotiate the cash price of the rig you want first, do not even mention a trade. Also, if it is a large dealer try negotiating on the last day of the month, preferably in the afternoon. They will have, in all probability made their nut for the month and anything else they move by the end of the business day generates cash back from the corporate office.
After being offered $4,500 in trade for our 22' TT I told them no but called them out on the above scenario (it was July 31st). I asked the sales manager (at La Mesa RV), to tell me I was wrong and he declined to do so. Told him I would buy the Class C that we had already negotiated a good cash price on but only with a fair value on the trade.
They balked and we walked {out of the little office, they hate it when you do that}, and stood by our truck for a few minutes. My wife asked "What happens now?" and I replied "Wait for it."
About 5 minutes later they had "made a few calls" and found a buyer for our TT and upped the trade in to $8,500 (which is what I had it consigned for at another dealer.)
We made the deal and believe me they made money, but we got exactly what we
wanted. It worked for us and just might for you. Remember... From sex to sales, nothing beats asking. It is free with just two possible answers (only one of which is bad). You don't ask, you don't get.
:B