A good starting point is NADA RV Guides. Since yours is a 2012 model, you'll find an accurate listing. But beware, the values quoted may be quite high or low depending on your circumstances. When we traded in our FW a couple of years ago, the NADA guide said it was worth $17K, which sounded about right to me. However, when I traded it in, the dealer offered me $27K which surprised the heck out of me. This was after they'd already quoted me a reasonable price on our new one. I made sure I signed the contract right away before they took the offer off the table!
NADA RV GuideJim