DPX170 and 171 say not to spray over media blasted metal, and not to topcoat with epoxy. DX1791 is not to be used over media blasted metal, either, but may be topcoated with epoxy. Why would one want to spend the money on quality products, and go against the advisement of the manufacturer? They put the resources into testing their products, but you think you know better? I'm not saying you are wrong, but I would think the manufacturer has good reasons for their recommendations, and I don't have the resources or knowledge to be able to disagree with them. Does anyone know why they recommend the opposite of what others here are doing? This is what PPG says about DP40 Epoxy Primer: Film build of 1.2–1.5 mils of DPLF is required or the surface must be treated with Metal Cleaner/Conditioner or coated with DX 1791/1792 [self etch/wash primer]. You can't do both, though. I don't have any recent experience with automotive coatings. Many here have experience, and apparently haven't had problems going against the recommendations of the manufacturers, but without knowing the reasons for their recommendations, and under what conditions you could have success deviating from them, I wouldn't.