Powdercoating is like doing a paint job. The job done depends on the prep work before. My buddy has a powdercoating business and has done plenty of stuff for me. He always makes sure the parts are bead blasted clean and pre heated for better adhesion. Pre heating most all parts is really the secret. It allows for any porosity in the metal to dissipate out so when the powder is applied, it flows on nice and smooth and is bonded to the metal.
If a scratch or chip does happen on anything coated you can touch it up with paint to stop any moisture from creating rust as well.