We got our Sonoma at year end pricing, and, like buying a car at the end of a month when a dealer is trying to make his quota and control flooring costs, it came out a little better for us.  

Perhaps the best way to test the secondhand trailer market is to do a test ad with your dream price.  If you sell it, fantastic.  If not, wait a few weeks, then put it in at a lower price and see what the interest is.  Always ask more than you're willing to take and be willing to negotiate without being insulted when someone gives you a low ball offer.  Simply thank them and say you would be willing to go to $x, still leaving some wiggle room.  If the person is interested s/he'll counter.  If not, then move on to another buyer.  That is going to give you the best sense of the market into which you are trying to sell your trailer.  

The bad news is that Craigslist is now charging $5 for posting rv ads.  But at least it gets rid of some of the clutter.

Time of year is also important. Dealers are putting out great savings from mid-October on to rid the onsite inventory. Spring is when folks are thinking about camping and the dealers have current stock coming in. If always looked at Spring/mid-summer to be the sellers market and late-summer/fall as being a buyers market.

There's always exceptions to any rule...

Google your trailer and you see several sites in which to compare pricing.