After discussing this with Dennis Drumheller on Saturday, and entertaining his thoughtful suggestions, I still went with Plan A. But I'm glad we talked about it. With Dave Santos' help, we muscled the 1/8' Masonite, smooth side towards the layout, and glued/screwed it in place. You really needed a second person to get it in place around those tight curves on the left. I also trimmed the fascia around each end's scenery formation. Once it was fastened, I sealed any gaps with hot glue. There was some carpentry done for additional fascia supports before we did all this. So while it may not look like a lot, there's a Train Night!