Some of the dome cars are tricky, I end up using #30 wirewrap wire in either black, white, or clear to sneak up to the dome to drive the lights. In extreme cases, I have at least four different small LED strip segments, all wired with the fine wire to get the job done. As it happens, other than the fact that there's no place to run the track power under the floor, these SuperLiner cars are very easy. I had a K-Line dome car with no place to put lights on the dome, so I did floor lighting on that one, it actually worked out really nice.
In all cases, I try to install the lighting so that you can completely separate the various parts of the car for maintenance, it really drives me nuts when I open a passenger car and I have spaghetti wiring stringing between the parts! 
I also get the same reaction when I open an upgraded locomotive and the shell is wired permanently to the chassis. What in the world were the people thinking???
