Hi, Joe! Itís not obvious from the forum title
, but all the trailers here are molded
fiberglass, meaning they are built by spraying fiberglass into trailer-size molds (think egg-style trailers like Scamp
and Casita). Thatís different than framed trailers covered with a skin of aluminum or composite sheets.
Off-hand Iíd say aluminum is lighter and stands up better to intense sun, but itís more easily dented by rocks and hail. Fiberglass deteriorates in UV, so itís important to store it under cover and/or keep a good coat of wax on it. Smooth fiberglass will give it a more modern look, while aluminum preserves the vintage style. No idea about cost. Both share the same issues with proper sealing and maintenance of the seams. Thatís one reason many of us have gone the molded route.
You might get more and better advice on the vintage trailer site tincantourists.com. Best wishes with your project!