Do I paint in halves or wholes?

       I am currently building the MRC version of the UH-1C huey heavy hog model and I am almost done,I will be modeling it with all the doors open, but I am confused as to whether or not to paint the fuselage in halves before the model is done or do I paint it after everything is assembled? If I paint it after it's put together, how do I keep all the paint out of the areas it's not supposed to be in? If I paint it before I glue it, then how do I fill the join lines between the halves without messing up the paint? This is the only thing stopping me from completion.