cast iron tub - refinishing exterior - suggestions?

[kavita]

g'morning all -

i'm refinishing the exterior of a cast iron clawfoot tub.

it appears to have a coat of latex paint on it now, over the primer. the paint is in fairly good condition but i'd like to change the color.

there are a very few, small areas where rust pock marks have appeared through the paint.

i've refinished tubs before (sanding, priming with rust oleum primer, top coat of rust oleum paint) but someone recently told me it's okay to use latex wallpaint as a top coat.

has anyone had experience with using non-oil-based paint as a topcoat on a cast iron bathtub?

i love the ease and clean-up of latex, but i can't imagine using a waterbased paint over cast iron - even with the presence of an oil-based primer.

your experiences?

many thanks, kavita