its probably the shitty primer you are using. being from a can it may be lacquer? Also it is wrinkling around your sanding marks because you are putting it on too heavy or something is contaminating the surface. It needs to be stripped completely, dewaxed and degreased, and put down some adhesion promoter and some type of plastic sealer/primer, then sanded, then I would seal it again, the paint it. It may work. But have it done professionally.