it depends if the rail is pvc dont but is it is metal paint it. i would suggest snading the pipe down till its super smooth then using a sylcone paint or something that leaves a super smooth finish on the metal. i would suggest home depot for finding the paint or a paint speciality shop.
yeah fuck that shit when you slide the rail the paint will just come off. I painted a skate rail then sanded the top until it was smooth as fuck. Then I waxed it to. Paint slows you down.