What I decided to do was board the opening up. This will hide that over thick wall just fine. I found a photo of a sheet of plywood online and reduced it to scale. I made a copy grayscale for the outside piece. This will be on the hidden side – visible only if I slap my keyfob camera on a flatcar and run it past. I cut out one of the spare window frames from the kit and glued the plywood to that. For the inside I used the colored plywood sheet. There is a watermark just visible .. which .. shrug .. is fine. Something was painted on the plywood .. fine with me. If it bothers me when the inside plywood is glued on the building I will put something over it like a calendar.
The wall they are sitting on in the photo is the wall that will face the aisle. You can’t see that inside wall when the building is in place so I’ll install probably put a Tichy window there to light up the inside of the building.