When we struck a deal for our Class C agreeing on an aggressive "internet cash" price I told them I would not buy it until my TT was gone. They offered $5400 in trade (sight unseen), which was the wholesale price out of the dealers book. I told them firmly 'NO!" and walked out of the little room in the sales department (they hate it when that happens). :B
Our TT was immaculate and very well equipped. We had it on consignment at another dealer with it listed at $9,500. The consignment dealer expected to easily/quickly get $9,000 and I would receive $8,500. I showed the Class C dealer (La Mesa RV), pics off the TT and 5 minutes later they came scrambling out agreeing to up the trade in to $8,500. I am certain they sold out TT that weekend for at leas $9,000 probably a little more.
By doing the trade in the sales tax was computed on the difference between what we traded and what we purchased saving us about $600. The consignment dealer wished us well and I went back on Monday and delivered a case of good (ice cold) beer and $100 for his time and trouble (not much of either but it seemed like the right thing to do).
A couple of thoughts: Our deal was done in Arizona so the tax break may or may not be available where you are shopping. Just because they quote you a ridiculous low ball trade value does not mean they won't come up, especially if it is on a clean easily resale able rig. Always negotiate your very best "cash" price on the new RV before even mentioning any possible trade, no sense playing all of your cards too early. Yes, they howled when I insisted on doing the trade at the higher price but bottom line they made money about 4 ways to Sunday.
Lastly, we were haggling on the afternoon of July 31st. Just about any large dealer has already made their nut for the month at that point and anything else they move is pure gravy from the corporate office. :C