The answer is, it's not easy and you need to take your time. It's hard edged at least, so you can use a brush.
You are right- masking and spraying installed railings isnt going to work. Other single colored subassemblies are easier.
If you spray what you can, and then install the rest and brush, you should be fine. I find that ship models are pretty much brush jobs except the bigger areas.
Does Gator make a mask set?
Edit: Gator does. That'll really help.