Reply:  If looked after and installed properly, the stove will not rust.
If rust appears on the stove, it is usually because the stove has been exposed to moisture, possibly from the chimney.
In summerhouses, the temperature is often very cold in winter and the still air in the combustion chamber can cause condensation on the stove surface. You should therefore leave the valves in the stove open to prevent condensation forming on the oven, which can cause rust.