Yes, you can apply RustSeal over another coating. You want to be sure the other coating is fully cured, and if glossy, the coating has been slightly scuffed with 320 grit, and cleaned well with KBS Klean. This proper preparation of the old coating ensures long-lasting adhesion. If the old coating is not adhered well to the surface, wire wheel the old coating to remove any sections that are loose before prepping the surface.
PRO TIP: As with building a house, the foundation of your painting project is critically important. RustSeal provides a solid, long-lasting rust prevention foundation when it is applied directly to the prepped surface. When you place other coatings in between RustSeal and the surface or substrate, you are relying on the other coating to be your foundation. That said, we understand that it is not always possible or feasible to apply RustSeal to a prepped bare surface, so applying RustSeal to another coating is always a great option.
Please review the complete RustSeal Application Directions before you begin your project.