Just had a few more thoughts.
Zinc is a reasonably ductile metal so will flex as the chassis does so little likelihood of cracks, which can occur with other brittle finishes.
Mixing different metals is also an area to avoid without a physical barrier between. Corrosion is an elctrochemical process and each metal has a different rating. This difference causes a corrosion cell to form when an elctrolyte is present - eg water or worse still, salty water! So, a coating to keep water at bay is also reccomended.
