Sand with a 7 inch disk sander where you can down to bright unoxidized steel
. Don't torture yourself with a wire brush. Use an epoxy sealer like Interlux
2000 which can be put straight over clean unoxidized bare metal. Don't put any sort of anti-corrosion chemicals over the bare metal that might reduce the epoxies ability to adhere. Put a number of coats over your original coat to build up the thickness, and therefore resistivity to something scratching it down to the bare metal. Interlux
2000 is very tough and its sandable. Use an epoxy filler to do the fairing with another 2 coats of Interlux 2000 over the filler. Antifoulant paint can be rolled right over the 2000.