I would first try posting it for sale in the Classifieds on these Forums. You will find the link along the top tool bar. You need to prepare for the listing by checking out the prices of similar units so that you will know where your asking price should be. Check out NADA and ebay to try to find some comparables.
Once you come up with an asking price, you will need to take a bunch of digital photos of both the inside and outside of the unit. Take all photos at the lowest resolution on the camera so that they can be easily posted and emailed. If you don't do a lot of good photos, it probably won't sell.
To get the best price, you will need to clean everything up and make it look really sharp. You need to test all systems and make sure that everything is in working order. You will be asked about this.
This is not like selling a car. It will be a lot of work for you. Make sure that you are ready for it.
Good luck. If you have any questions, please do not hesitate to ask. You will get good, solid answers here
SuEllyn & Brian McCabe
WBCCI #3628 -- AIR #14872 -- TAC #FL-7
2015 FC 25' FB (Lucy) with HAHA
2020 Silverado 2500 (Vivian)