Galvanizing, powder coating will not penetrate. If I have a part like this I will apply a product called Penatrol in the problem areas after they have been galvanized, or powder coated. It is a paint additive but also is a excellent sealer and rust inhibitor. It can be found at Home Depot in the paint area. There is a sound alike product. Make sure you get Penatrol, the other is not the same and will not work. Not sure if it is available in the UK?