Newby - to plate or not to plate

[timmyville1]

This is my first post so I apologize in advance for any missteps on my part. I am building a 1.5" scale live steam locomotive. Most of the components are mild steel. I plan on painting parts as it is assembled because most of the parts become inaccessible once they are on the engine. It is going to be a warm, steamy, wet, environment and I am worried about rust getting started when the paint chips (this is going to be a working loco and although I am careful, scratches and chips are inevitable) - paint touch up will be difficult. It it practical to use some kind of plating/metal treatment under the primer/paint to protect the metal from rust if the paint is chipped or scratched? thx, timmy