I used a 2 part epoxy bathtub paint that I purchased at Sherwin Williams.
I am sorry I don't remember the name but I am sure you won't have trouble finding an epoxy tub/tile paint. I painted the fiberglass tub and the plastic lavatory. I did spray it. The box says you can brush it but I did not like the results. You will have to thin it just a little more to spray it but the results I got were great. Also, the fumes are very strong so a charcoal filter mask is a must. After 4 years of use, my bath still looks great with no chips or discoloration. If you do have a chip or mess up spraying it you can let it dry for a couple days to fully cure, wet sand it with a 320 wet paper and respray.
Bruce & Rachel
68 Trade Wind
2001 Toyota Tundra