I’m looking for the best possible prep/primer solution for older cars that have been stripped to bare steel. Often, there are small, maybe even barely detectable spots of surface rust that seem to cause blistering even under a self-etching primer. I’ve used POR-15 and had problems with shrinkage. Will Rust Encapsulator adhere well without chemical treatment? Can polyester fillers be applied over the primer? What kind of primer surfacers work best with this product, polyester or urethane?