Plastic tub refinishing - any suggestions?

I am embarking on a remodel of my TT and the tub is in some need of some TLC. It's still in great shape (no cracks, etc...), but the color has faded and I would like to refinish it to freshen it up a bit.Last year I had to take the tub out due to a cracked P-trap and I did a little test on the underside to see if it could be painted.

I scuffed an area on the unserside with some sand paper, wiped it down with some isopropyl alcohol and have it a couple coat of rustoleum white paint for plastic. I allowed to to cure and was very disappointed when I could pretty easily scratch the paint off.

So does anyone out there have a suggestion for a durable way to refinish my tub?