Because I am doing a rust buble on the roof of my van. I don't have any spray guns or compressors. So am going to paint on epoxy primer by brush. It's only about 2.5 inch wide repair. Removed all rust and feathered the repair. Just worried by brushing on it and sanding it back might not be able to get it exactly flat with existing paint before top coating.
a bit more effort sanding the epoxy with a block would make for a better job , but yeah if you want to use rattle can primer it wont hurt as long as you keep it dry , dont be driving or parking it out in the rain