Depending on the value of the trade-in, you want to also consider the sales-tax benefit, if your state allows. If you have a trade worth $10,000, if you have a 5% state sales tax, you will save $500 when you go to get the tags, if you trade. If you sell it privately, you lose that sales tax "credit", so you must sell it for much more than $500 over the trade value to make it worth your time.
Every sale is different, as each market is different. I sold a 2-yr old TrailManor for $17k. I paid $20k for it new. Dealer would give me $10k for trade.
I received cash from the buyer (through Craigslist, listed for three weeks). I was fortunate that I had a rare item, and the right buyer found my ad. If your trailer is similar to others on the market, your benefit from selling privately will likely be much less than mine. Just the difference in market.