You can buy a flat Aluminium paint in most DIY Shops. It has very little body to it which is why some use Hammerite to stop rust coming through.
The only problem with Hammerite is if it reacts with anything or if you want to get it off.
I found a tin of the correct fire resistant paint but the paint does rub off on your hands/clothes.
Remember also depending on when your vehicle was manufactured during WW2 it could have been white inside.