I was told by the dealer that they order the next model years trailers late summer and start getting them in in the fall. If that's true, then I'd think when ever the lot starts to fill up with the next years models you'd get a good deal on this years. Of course just like cars, it's a year old the day you buy it, resale wise. If you can buy last years after seeing this years.
Not that I've had many, but I figure out the trailer I want, research a fair price on the internet, and go talk to the dealer you want to do business with.