Whatever you use, make sure all the areas you treat are completely clean of any dirt, rust, debris. All these things (and more) trap moisture and when you 'coat' the undercarriage, you permit corrosion that will remain hidden until a failure at the location. This is why it is best to have any type of coating done at the factory and not at any dealerships. The transportation from the factory to the dealership you buy it at may expose the car to corrosive elements, which usually isn't completely removed upon application of an aftermarket undercoating. Just saying.