Dealers make more money selling new units plus they make more from the factory warranty work. It may languish on their lot forever, or at least for a very long time. You sure don't want that if you need the cash for the next TT.
A dealer will want to price it at the blue book value no matter how much you've upgraded it or if it is in pristine shape. I would sell privately but the question is where to list it. There are consignment lots that sell just used RVs, but I don't know if they are any good.
We sold a previous TT to my BIL who got the benefit of several thousand $$ in mods and upgrades but we couldn't get more than what it was worth on the open market. We had no bites on CL after several months which was getting discouraging.