Bodywork rust repair question.
 

I have half a dozen quarter size surface rust spots at the bottom of a door. Before taking it to a bodyshop for this and some other paint and bodywork, I want to do most of the prep work to save some money. I used my new Vacula Rust-Eater spot sandblaster to remove the rust down to clean bare metal. Since the former rusted areas are pitted, I need to apply a thin coat of body filler. The question is do I first spray some etch prime on the bare metal and then apply filler or can I just spread the filler over the bare metal and then cover it with primer?

Read the instructions on the can - but before you do anything talk to the bodyshop you're going to go to. If they're going to finish the job you need to make sure everything you do is compatible with what they are going to do. In other words the paint needs to be compatible with the primer - just as an example.