I've seen a chart for this somewhere before. I Can't find it right now, but I think it basically said if you sell a travel trailer within 3 years, you would lose less than 20% of the original value....assuming you maintain your trailer well.
I originally bought a TT because I was leaving SoCal and wanted to see the country. I had a 90lb lab and a girlfriend and we didn't want to stay in hotels everywhere or risk tent camping in October in Oregon or Washington. My original plan was to buy it, use it for 3 months, get back to Maryland and sell it. At that time, it would've still been 2007 and I had a 2008 trailer to sell. Instead, we fell in love with RVing and kept it until we just traded it in a couple months ago. I guarantee I could have sold that thing for close to what I paid even if I had kept it for a year.
The beauty of the trailer is that it doesn't track miles. I lived in my 2008 for 8 months after traveling in it for 3, plus my normal camping use over 7 years and when I traded it in the dealer said it was spotless and the cleanest trade in he had in years.
In the end the value lies in the maintenance.
2010 Chevy Tahoe & 2015 Keystone Bullet Premier 30'