My kids are not quite as old, but at 10 and 12 we're into the 'travel ball' years. Our camping trips look a lot different now then when they were younger. Often they are to some God forsaken middle of nowhere town (where the softball tournament happens to be), but it's still fun to take the RV instead of hotelling it like everyone else.
We only get out every other month or so, but its totally worth it for the few times we DO get out.
I've sold and bought a lot of stuff on Craigslist, and that's how I would sell the trailer if I needed to. My personal approach is to clean stuff up real good, price it slightly low, and get it done quick. If it won't sell for what it's worth, then you may not know what it's worth. :B