Regardless of the age there are certain things you need to check when buying a used travel trailer and this link sums it up nice.
Most trailer over 15 years old are going to have some issues. At 15 years age most will only have 10 years use left in them unless you spend a little keeping them in good condition. While a vintage is nice ongoing repairs can make them a costly option to own. I wanted one but opted for a good used one instead that had more room and modern amenities' .