I've managed to get the plug for the 41 foot roof finished. I'm calling it a plug because I'm going to use it to make a mold for a fiberglass part. Fiberglass is not customarily used in model railroading, but I don't see why it won't make a great passenger car roof. The following video gives a little tour of the around the plug so far. . . .
Tonight I am going to paint it, and begin prepping it for mold making.