where you have your top tube/seat tube this is where your legs will rub agest it, and will wear off the fastist, but you can always just get a spray can of paint laquar to go over it every 4 or so months
The cromoly frame is lacquered and won't rust unless rubbed off. This can happen on vulnerable parts of the frame such as the chainstays so keep an eye on them as corrosion can occur there.