The question is how long before you are going to paint the car. Primer is pourous and can let moisture under the surface, this would mean you would have to strip it back before you paint. Depending on the primer I think you have about 100 days to paint the surface.
I have been using a phosphoric acid called rust buster, when applied to bare metal it creates a chemical barrier and stops the surface rust from forming.Por15 also do a product that applies a wax type covering and they say it can be driven outside for 12 months as long as the wax layer stays in place.
Just on wax and grease, (prepsol) I went on a course run by a professional car show painter and he recommends using acetone instead of wax and grease. The main reason was that wax and grease can still leave a film while acetone totally evaporates. The other thing is that it is about half the price of wax and grease.
Hope that helps
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