Hello,
I have a weathered letterbox. It's metal and been painted or powder coated (?). As can be seen in the photos below, some of the paint has come off.
I'd like to paint it. I was planning on just using a paint brush (vs spraying or the like). I was going to use some Dulux Weathershield that I have left over.
What prep do I need to do? Just a rough sand back? Sand back to bare metal? Do I need to undercoat, if so, what should I use?
Thanks!

