I use acrylic enamel from a rattle can. The two brands that I have found to be the best at coverage and durability are rustoleum and surprisingly Ace Hardware's "in house" brand. It takes about 2 to 3 medium coats to get good coverage. Pre-cleaning real well before painting is very important and it is important to remove any excess silicone from around the edges. It is common for the paint to want to fish eye where there is, or has been silicone, I just do multiple dry coats in these areas so the paint can't separate. I would suggest using a gloss paint because it doesn't seem to want to absorb salt and salt creep as much as the flat finishes do. All my tanks at the shop are painted, they have held up pretty well.
Joel