I had the same issue with utilities in my train room. Before installing the ceiling, I took pictures of everything so I would know where everything is in the event of a problem. There are a few cleanouts in the ceiling (not over the layout thank goodness), but if I ever need to get to them, I can locate them and will make access panels in the unlikely event I would have to get into the ceiling. Just a thought.
Either way, it looks like it will be a great train room. Keep up the great work.