That's the way i have done it also. Put a coat of black paint over it. That way the undercoat will not crack... this is the best solution to prevent cracks,Bruce said:I used Corroless (similar to POR-15) followed by a coat or two of rubberized undercoating. I usually prefer 3M products but I use the Mar-Hyde undercoating as it seems to be better. I also put a coat of black paint on it after it has dried for a couple of days.