Clear coat/ plasticoat
Yes, the '69 Airstreams would have been factory Plasticoated; and when the Plasticoat fails it will take on a "milky" appearance. The plus is that the aluminum has been protected from the elements, but before the trailer can be polished it will need to have the Plasticoat stripped. I recently had my '64 Overlander professionally stripped, polished, and re-Plasticoated. Generally, the price for this service runs in the range of $150 to $175 per linear foot. True Plasticoating is only done by a select few refinishers nation-wide as it is a very particular process - - the Ruth's of P & S Trailer Service handled the details on my Overlander.
Good luck with your investigation!
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)