You will take a hit on a trade but selling yourself is a******shoot. Could sell in days or could take months. A trailer that new could be a tough sell because you will be priced close to brand new models.
Dealer pays wholesale because they have to deal with the pitfalls and risk of selling your trailer.
Selling your self will net you the most cash but you have to take the time and effort to sell it.
Trading is convenient but you will take a bigger financial hit.
Upgrading/changing a 2 year old RV is doable but is generally a losing proposition.