To paint over ANY surface, without sanding, use a product called 'ESP Easy Surface Prep', available at hardware and paint shops. Wipe on, wipe off and paint in 90 minutes. Works well over enamel paint, without having to sand. SAVES HOURS of work. It was recommended to me by a professional painter.
Hate cleaning shower doors check this out! This was obviously designed by a woman! Glass-less. no cleaning the shower door! And 2 sides with separate shower heads in case you & spouse both have to get ready at the same time! I need this shower