Wire brush first. I use a cup style wire wheel in a 4" grinder. It is a rust eating machine. You need a full face mask when doing this, or you will spend half your time digging crap out of your eyes. Next coat everything in rust converter. Final step, coat everything in "Fluid Film". It's available from Amazon, and it is damn close to magic in a can, when it comes to preventing future rust damage. My son runs a shop that does heavy equipment repair, that use shit-loads of the stuff to protect their equipment. It's nasty to apply, and makes the car smell like a wet dog for a while, but if applied regularly it will keep new vehicles from rotting, and stop next year's rot on older cars, even where you live.