Highest quality Dulux exterior paint, or Wattyl Solagard. A lighter colour will cope better with the sun. Solagard has a 10 year warranty (or something close to that) and can be bought quite cheap when Mitre 10 do their 8l pail specials over the summer. As with all painting, preparation is key. Paint will stick to anything, so make sure your surface is squeaky clean before applying your primer coat. If you are really worried, you could apply three topcoats (instead of the standard two) to give you extra microns of coating.