:confused:
Are you going to be able to place caps on them? If not you can try this, since you cannot see inside the part, you can just leave them primed with a good primer.
Get yourself an old fashioned glass cleaner the man made sponge type, tie a sturdy sting aroung the middle or tie it to the hole on the end of the handle. Place the side rail on a angle so as to lean away from the rest of the parts, dip the GC in the primer or paint and pull it through the part you should start from bottom to top so you can control the speed, once dry do it again just to be sure. Does this make any since to you?