Airstream travel trailers were first put on the market in 1932 but have become increasingly popular in the first decade of the 21st century as restored recreational vehicles. Such a restoration project can be expensive if you want authentic parts and a purely vintage look, but simply restoring an Airstream to usability is a cheaper process.
Check the floors for rotten wood or peeling veneer tiles by stepping heavily on the surfaces. The quality of the flooring is poor and needs to be replaced if your steps reveal a very soft or squeaky surface. Rotten flooring can lead to further structural damage in your Airstream. Replace the flooring as needed.
Look over the framing of the undercarriage and the walls of the trailer's interior for any significant deficiencies, such as large holes or rust spots. Sand down any rust and treat it with a coat or two of rust-retardant paint. Fix wall holes with drywall patches or replace the wall entirely.
Remove any additions from previous owners if you want an authentic Airstream travel trailer structure.