We have all seen those electrical conductive paints (50 ml for $20 and up.). Well I was thinking this could be made easily and much cheaper since carbon is a conductive material. You can purchase activated carbon pellets (40 oz bottle for about $10 US) from pet stores which are used in filters for fish tanks. Using a spice grinder to turn it into fine powder. (You now have 1182 ml for $10) (Make sure to do this in a well ventilated area using filter masks as the dust is toxic and flammable). Mix with glue and paint the lines on the interior side to the lighting locations on the model and attach the leds and battery wiring. The glue helps bind it into the paper fibers. Could also use caulking for flexibility as needed.