The aluminum skin will usually look to be in good repair. The issue is the condition of a 20 year old steel frame, and how well the flooring is holding up. These areas should be especially inspected for rust, rot and damage. Look around the edges of the aluminum skin, where it is affixed to the frame. If you see any greyish or white powder, open holes or pits, walk away and look for another trailer.

Check every hinge, latch and door fit. Purchasing body repair parts for some older trailers can be difficult.

Brakes and bearings on that age of a trailer, should have been replaced at least once by now. If they haven't recently been upgraded, you can expect to have them replaced. Tire condition is important, and depending on the axle weight and tire size, replacements can be expensive.

Most LQ components are readily available, and can be individually obtained from many sources. Check them all for proper opperation. You may find the cabinet doors have well worn hinges and latches. They can easily be repaired as a DIY project.