Hi, I restore cars for a living and am very impressed with a product called rust destroyer which is basically a special primer that killed rust and corrosion and it can be applied on various metals including galvanized metal. I've used it on galvenized a number of times with great results, it far exceeds its guarantees.
By the way I hope you are welding that stuff in a well ventilated area, the fumes from galvanized metal are known to have killed people almost instantly. I always have a fan nearby when I weld any toxic metal, as well as the big shop blower vent on with a door open at the opposite end. Goodluck ~~Metalman~~