Trolley/streetcar/LRV body materials

[Swadian Hardcore]

Been wondering about the bodywork of trolleys and LRV's while researching bus/train bodywork. What materials are used to construct the bodies of trolleys? What material was used for the Peter Witts, PCC's, and modern LRV's? Why don't we see stainless steel LRV's the same way we see it on intercity trains?

Thanks.