I do a lot of Freight and Passenger car scratch building I try
to put as much detail as I can into each car.
How ever when it comes to Flat cars and Gondolas that have
fishbelly sides that completely hide any under body detail I
leave it out, except for the center sills and cross members.
So, my bottom line is if you can't see it I don't model it. This
leaves me more time to do the fine detail that you can see.