You need a paint that can fuse with and flex with the vinyl. I'm not much of a painter but Krylon Fusion in an aerosol can is made specifically for painting hard vinyls, plastics etc. & in my experience holds up well on flexible vinyl surfaces. Call around to your local hardware stores, only about half of my local stores carry Krylon Fusion. Not to mention that Krylon in general seems to give a better end result with less tendency to drip like Rustoleum does. Don't use regular spray paints, they'll start flaking off.