I use and like Klass Kote primer too. It's a favorite paint underlayment because it sands so easily and feathers great. The only complaint is that it is heavy and I find myself sanding almost all of it off. Only primer left is in the brush marks and still the gain is about 15 grams per panel. I didn't use a block this time either and I think it worked better since I was in touch with the surface continuously.

Since yellow is the main color of my panels which covers poorly, silvering over the sanded primer is a must producing an even colored surface to shoot yellow over. I used rattle can silver from Home Depot. It dried within a few minutes and it covered great. In fact I used only 3 grams per panel of silver to cover almost 1000 squares of each panel. That's almost nothing and worth the weight investment. We'll see how much yellow will be needed to cover that.....