I think stick built refers to wood studded walls rather than aluminum studs. Generally the lower cost trailers have wood, moderate to higher priced have aluminum but there are exceptions.
Our current Winnebago fiver has a gelcoat fiberglass, high gloss and looks great. Very easy to keep clean and waxed.
Not sure what our prior trailer had. It was lower cost with a smooth but not high gloss finish. Looked to me like a very thin plastic sheeting. After 9 years it still looked great but nowheres near as nice as the gelcoat.
The biggest problem I've had with the corrugated aluminum siding is how easy it dents. Small little nicks and dings show up quickly.