If the shell is water tight prior to parking it you could probably get a good 10-30 years out of it. Mine is 35 years old and was parked at the coast for 7 years before I bought it. Parking an Airstream is about the worst thing you can do to it, they were designed to keep on rolling. The axles will go bad, then the shell will start to leak, then the floor and frames start rotting out, the windows leak, etc. With some minimal maintenance every few years I could see it lasting 40+ years if parked. I have a 1981 model that I will be parking because it isn't worth doing a frame off on it. I plan to rework all the sealants prior to parking it and then do maintenance on it every couple of years as needed.