I sprayed with a low pressure system outside a mates builders van in white in the UK about 20 years ago in hammerite its ok if you stand about 5 miles away. another mate rolled his estate in blue hammerite, tryed to wet and dry it that did not look good even from 5 miles.That link was brilliant Bungle.
I am hoping to paint mine with smooth red Hammerite. Just need to work out the thinning and if it will roll on well.
so think about it. try some diffrent paints on old panels. let them dry and see what happens.