Exterior and Interior paints are manufactured to hold up to the elements they are meant to be applied in. An interior paint used as a first coat on an exterior application with an exterior paint applied over that is just trouble. It will not last and you will have bubbling paint because the interior coating will not hold up. Even with a top coat of exterior on it.
I know sometimes like SW can get confusing when using Super Paint because they make both Interior and Exterior for the same name. Thats why i always check, check and recheck all the labels. We actually had new people at the paint stores shoot an exterior color for an interior paint and vica versa.