We sold our High Country recently in two days on RV Trader. Spend some time
really cleaning, detailing your trailer. Take some GOOD photos (or get someone to help if needed) and write up a well worded, descriptive ad. It's surprising to me how little effort some folks put into their ads...
You may get calls from various "brokers" once you place your ad on RV Trader however...I had one especially annoying and pushy salesman who insisted I would NEVER sell my trailer that way.
Of course the first person to see it bought it two days later!
Craigslist is free, but you do get a lot of trolls and scammers that way too so be careful.
Good luck with it!