I wanna raptor line my bumpers--they have spots of rust and a layer of spray on bed liner. What should I do for prep work? Wire brush to knock off rust and spray with primer?

Need advice from anyone who's done before

 

Take a angle grinder with a wire cup to the bumper to knock everything off. Prime then spray the raptor liner.

 

There is no better prep than a sand or shot blast with a solvent wipedown to get rid of any moisture from the compressed air used during the blast. Wire wheels tend to polish the surface of the metal eliminating the rough texture required for a good MECHANICAL bond. Doesn't matter how good a coating is with the CHEMICAL bond if the surface being coated is as slick a snot on a stick.