Chet, I saw that Rustoleum is advertising a new product for painting bath tubs and sinks. If memory serves, they call it something like C&C paint. As far as I know anyway, it is a new product and I haven't seen it on the shelves here yet, but then I wasn't specifically looking for it.
Just based on the brands track record, I believe that I would wait until this was available and give it a try. I'm sure that they will have prep instructions on the label.