Assuming the paint on the metal cabinet is clean, fully cured, dry, sound and prepared as detailed in the technical data sheet we can recommend Hydron Nu-Guard AG.

This is a single pack external coating designed to give effective protection against both fly-posting and graffiti.

This is available in clear and also a range of colours in a semi-matt finish.

We would recommend to test on a small area prior to full application for compatibility and adhesion.