You can paint it, have done so with the rear crossmember of my galv chassis. I coated it with mordant solution, sometimes known as T Wash, leave it for a couple of hours and it will go black. Then wash it off, allow it to dry then I sprayed an etch primer, then I sprayed it with Pro cote primer, then a satin black and its come up well. Companies that provide galv bulkheads wouldn't be too popular if every single one of their products lost the paint quickly.