sheet metal/paint technique question

How do you plan to do the metal repair without an air compressor? Do you have access to an air compressor? (Friend? Rental)? If so, here is an idea you can try. Get a cheap paint gun ($20) from harbor freight. Buy a quart of a good filler primer that has corrosion resistant properties. I can suggest one from PPG. NCP 270. It has great filling properties, and awesome corrosion resistance. You can put it over bare metal and is a 9 out of 10 for corrosion resistance.

If you are going to take the time to do all of the bodywork and prime it with rattle can... you will eventually have to sand the rattle can primer off, or the bodyshop you hire will have to. Then you will have to prime with an appropriate primer. So why bother? Just do it correct the first time. The reason you don't want to prime with a rattle can primer is that when sanding it off again you will be affecting your body work. You will eventually break through the primer and start to sand into your already completed body work.

So, that being said, if you have access to an air compressor, do your body work, get a good primer, and spot prime each area. It will hold up just fine as long as it isn't seeing severe weather.

Lastly, etch primer is not meant or even recommended over body filler. It is "acid" based and eats its way into METAL. That is how it gets such good adhesion. It is put on very thin, "see through" coat. And has little to do with corrosion resistance. It's primary function is adhesion.