With the newer epoxy coatings, I would use one of them. The coal tar epoxy is cheap enough I suppose. You can go on up to 16 mils thick. However you wont achieve anything but a flat finish. It has all the soil, salt and chemical resistance your look for granted, but I would like something with at least a satin or more sheen. Remember with most coal tar 2 component epoxies there is a 10 to 15 minute induction time after you mix the two together. Usual pot life is 4 hrs, so have your act together. The product will go directly over metal or can be used on top of an appropriate primer.