I painted mine years ago. The majority of it with an airbrush as it had been down for a few years. I always weathered my structures and then started doing rolling stock an engines. The rails just had to be done as they really stood out being the only thing left shiny. Track changes that were made were painted outside with rattle cans. If you want to go down this road. Outside on a nice day before the track is laid is the way to go. If the track is already down. The airbrushing in place works but it helps to have a helper if it involves climbing on the layout. To either pass you fresh paint or to aid in the wiping off of the rails. Use an airbrush that will except a bottle so you don’t have to refill often. Paasche makes a good one that’s simple and user friendly. No need to mask anything off. It will all blend in.
As mentioned. Only worry about painting what you can see while viewing the trains run if your doing it with the track in place.
