I believe Streamlines used anodized aluminum (some, if not all years?)...but I'm not sure. You may be able to glean some Streamline specific info here: Houston Chapter Streamline Royal Rovers
. Not sure how active that website is - but Tom Patterson has a Streamline & he's always been real helpful to the vintage trailer community. You may also want to inquire with the Tin Can Tourists
group...they have members with lots of great (non-Airstream) vintage trailer members as well if you don't find what you're looking for here.