I use an Evercoat product called Metal to Metal on all the welded seams and any areas that have pitting from rust apparant after the sandblasting. It is waterproof and allegedly won't even allow air to get at the metal. I also use it on welded joints when molding a frame. Used it for years, even back when it was called Alumilead..... I'm sure they had to change the chemistry in the product to keep those meddling feds happy but I still am very satisfied with the results of using the new product.....