Top rust protection: zinc spray
Sand as much sand as possible, if possible sandblast (may have a buddy of yours), if necessary remove as much as possible with a sandpaper as clean as possible. Then remove dust with compressed air, etc. and make dilution with thinner (do not snuff too much!). Now mask the environment with a masking tape and newspaper and then apply the zinc spray, if possible in several layers. After drying you can then spray the car paint over it.
Is a super stuff the zinc spray. For years I have had a very stubborn, deep rust on the wheel arch, have now for about 3 years rest, not a Fitzelchen rust can be seen since then.
