Buying a rusty old trailer

Those steel cross members that support the floor are expensive as hell. Especially check the cross members around the tandems. New drivers blow a tire and keep going. Tire carcass beats the cross members=soft spot in the floor. Any kind of lexan/fiberglass roof is a pain in the butt to repair a water leak. Metal roof is the way to go. If you can pull the handle on your tandems easily and all the pins go in, I don't think you would have any problems.