Abstract: The invention relates to a method of manufacturing at least one hollow element of a fuel system (3), especially a casing of a fuel tank. It comprises the following steps: (a) introducing the element or elements to be treated into a treatment chamber (2) equipped with at least one microwave generator, (b) injecting a reaction gas into the chamber while enabling the gas to enter inside the said elements, (c) subjecting this gas to microwave radiation delivered by the microwave generator (4), at a frequency and intensity chosen so as to create a plasma in the chamber and to bring about the coating of a material, arising from the decomposition of the reaction gas, on the said element or elements, preferably on both the inner and outer faces of the said element or elements.