You're going to hate me for this...... Not only one bodger on this site!
When I built the LMS twins (late livery so in green with duck egg blue body stripe)I chickened out of building the interiors, apart from full cab detail. I painted the insides of the body side windows black. You'd be surprised at the number of plaudits I receive for the interior detail!
But, can I suggest that, if you are going to the trouble of including interior detail it might be worth considering lighting it on the inside? It's a great shame to spend so much time and effort on getting the interior detail right when it will be very difficult to see.
Brian