It is not recommended to use ZR on the topside or paint surface of panels. Although I think it is a stable product that can be sanded after curing, primed and painted, the manufacturer's rep discouraged it. I do not know how much more protection ZR will give you though on top panels under your color coat. You could always use ZR on your panels and then clear it with their crystal coat product for shiny side application. ZR is meant to be a direct to metal application so using it over old finish may not be the best application.