The most important thing is to get there an hour or so ahead of schedule, before the owner has had a chance to open her up and air her out. Walk in and close your eyes, breathe through your nose and smell. Does she smell damp, moldy, or too much airfreshner and artificial smells? If she smells damp and moldy, then you have a problem somewhere. Artificial fresheners are possibly used to cover nasty smells and damage due to wood rot.
Be prepared to be overwhelmed with all the systems, features and explainations from the owner; don't sweat the details just yet.
If it passes the smell test and you are still interested then if I were you I'd find an Airstream expert near you to inspect the trailer from stem to stern. Yes, this will cost you a couple of hundred or so, depending on how far they have to travel to get to the trailer, but could save you thousands of dollars in repairs to rusted out frames and outriggers or replacing a subfloor due to rot.
Per Mare, Per Terram and may all your campaigns be successful.
“It’s a recession when your neighbor loses his job; it’s a depression when you lose your own.” "Harry S Truman"