If you have a pole barn, your trouble are over.
The remaining clearcoat will be protected from UV rays, and you should see no more loss.
Do a detailed cleaning of the entire exterior, then use Walbernize to wax it, both where you have clearcoat and where it has failed.
Do this every year.
An Airstream kept under cover rarely exhibits the clearcoat failure that we see in those stored in the sun and rain.