Sanding epoxy primer just sucks. Unless it's like 6 months old and totally cured, it SUCKS. The "brush on" "I was impatient" coat of white primer on the cowls was terrible to sand. I went through 5 sanding sponges getting it leveled out. This has solidified the fact that won't be using epoxy primer ever again. I've ordered 2 different types of urethane 2K Primer that I'll be using from now on and may order a 3rd so I can have 3 separate color layers to make contouring and low spot hunting a process that goes 10 times faster with much less elbow grease than ever before. Right now I don't really need to do any heavy contouring, just final coat stuff so I bought a gallon of "buff" colored primer and also a "white" primer that will end up as my final topcoat. No more epoxy primer for 323 Composites. That's history.