Addressing some rust starting in my truck bed

[old Rusty C10]

having had many rusty trucks, i use a rust neutralizer then after that i coat with POR15 then a top coat . my local NAPA sells a permatex rust neutralizer that like mentioned above goes on white dries black If you use phosporic acid you have to make sure you neutralize that acid after its applied and clean the junk off otherwise it will rust again