They were pretty decent trailers and if the items Carl outlined are OK, should still serve you well. In addition, I would check the roof seams (chances are they need caulking) and look at the ceiling inside for signs of water staining, which would indicate leaks.
I would also plan on replacing the converter/charger too. The standard ones of that vintage were notorious for overcharing batteries and ruining them, often quite quickly. Replacing the converter with a modern, well regulated one is usually easy (depends on the type you have) and for a couple hundred bucks you can avoid future battery replacements and frequent (weekly!) checks of the water in the battery. IF you buy the trailer and decide you want to do that, ask further here about brands and types.