Keep clean, WAX, touch up chips- thats the plan.
I see some seriously rusty cars down here- not just Mercs but fords, BMW's, vauxhalls etc as well. My w210 has hardly any rust at all despite being here all its life though. Just a few small bubbles on the front wings which I easily got rid of.
The previous owner waxed it every few weeks. My old man does the same with his C180- again no rust.
The paint on these newer mercs is a joke compared to an old 190 though- thin, peely and nasty. If I paid any sort of money for the car I would feel bummed.