So it's been in storage for a total of 26 years? Ours was unsed for 28 years, and our #1 problem was the MOUSE HOUSES everywhere! The belly pan was FULL, the oven was full, behind the refrigerator was pack full. We found no live or dead mice just lots of what I called mice condos.
You don't want to breath in mouse poo, really bad for the lungs. Of course you can't tell if you have anything like that until you pull the belly pan off.
Check for rot in the usually places, near the front door, the floor directly under the ceiling vents, carpet can act as a sponge and if they have leaked, another mess, do a bounch test on the bath floor, this is where from what I have read here, is the most vunerable spot for floor rot.
We replace 8 feet of plywood flooring,stringers and outrigger in the front of ours and 6 feet of plywood, stringers, outriggers and frame in the back, all cause by water damage.
You say it's been in storage? Is that inside storage? If so, let's hope you are one of the lucky ones who will actually be able to buy an 70's airstream with no water problems anywhere. I got my figers crossed for ya!