The invention concerns a process for the production of hollow bodies of thermoplastic material, in particular a process for the production of fuel tanks of plastic material. In the process according to the invention preforms in web or band form of plasticised plastic material are shaped in a multi-part tool forming a mould cavity by expansion of the preforms and causing them to bear against the internal contour of the mould cavity. The process firstly includes the production of two mutually complementary intermediate products in the form of shell portions. Then respective built-in fitment components are secured to the respective insides of the shell portions, which face towards each other in the installation position, wherein at least some built-in fitment components of mutually complementary shell portions are respectively of mutually complementary configuration, in the sense that they can be joined to provide an assembled component or to provide a functional unit. The shell portions are assembled in such a way that the mutually complementary built-in fitment components engage into each other and/or come into operative connecting relationship with each other.