Well I'm pretty much done with my body work on my car. At least i think. My buddy has a whole gallon of some cheap Napa primer that I could use. I don't wanna spray the whole car with it, just the spots where I molded things to make sure the area is flat and smooth. Soon I'm gonna buy some good primer but wanted to know if after sanding, would spraying the good primer kind of defeat the purpose of it over this cheap stuff?