Matt: it is called "lost plastic". I am simulating a prewar sand cast Erie-Built. I know such a thing existed, because I have a sand cast roof and sand cast "fabricated" trucks. I did the B-17 windows with candle wax. I have since made them a lot more symmetrical.
I have no idea how I will do the chrome corrugations. And I will be inaccurate - Milwaukee had no Erie-Builts with B-17 windows and fabricated trucks.
I need another passenger train like I need a hole in the head - but I have a soft spot for that Skytop.