i used weld through primer on mine. the problem i found is that the start of the weld on the primer is difficult. the mig wont make a good contact with the metal the primer causes a slight film. the solution is to spray the weld primer on then once the two pieces are inplace with the primer between you scratch the hole area of the primer and then proceed the weld. after you are done i wash the area with a metal conditioner for extra protection. this will kill rust dead....