No primer, I only "spot" prime where I use the bondo. I find these paint stick awesome, just need to get the thinner ratio right. Each color is different and I use a hairdryer after each coat and I can run the paint under a tap and its very hard to remove when cured. I tried the Vallejo air one time in the past and it peeled off like a layer of rubber !
Also I seal them on with duplicolor acrylic lacquer and finish with Grumbacher matte varnish