We did this last summer but with a twist. I put our 2008 22' Pioneer Spirit TT on consignment with a local RV dealer that sells a lot of trailers in this size. I agreed to take $8,500 which was a good price for us as the TT was immaculate and well equipped. He agreed and listed it at $9,500 looking to sell it for $9,000.
In the mean time we made a strong cash offer on our dream Class C (a 2012 Nexus Phantom 23P with 6K miles), at another local RV dealership. They were quoting me $5,400 wholesale trade in and I just laughed at them, not going to happen. Told them I would not buy the C until the TT was gone and proceeded to start walking off the lot. Here in Arizona the sales tax is computed based upon the difference between the trade and the new purchase price. Suddenly they came up to the full $8,500 in trade to close the sale on the C and we saved $600 in sales tax.
I then put my 2006 F-150 Scab on Craigslist and the first guy to look at it bought at my full asking price. I miss that great truck but could not justify keeping it with nothing to tow.
Bottom line I recommend selling the TV and TT yourself but don't hesitate to negotiate with the dealer your buying from on a possible trade as there may be a tax advantage to doing so. It helps to haggle with a large dealer on the last day of the month as they have in all probability made their nut for the month and any additional sales are just gravy. Good luck!
:C