The Fiat Ducato and its variants do come with pre-drilled holes for the installation of a spare wheel carrier, and there are numerous parts suppliers online who offer a kit designed for this application for around £150. If you decide to do this job yourself, it is important to ensure the dimensions of your spare wheel will fit the space underneath and the carrier itself, and we would consider using thread lock on the key bolts to ensure it stays in place. We would also suggest considering the security of the wheel too, such as a locking nut or a bicycle security device for times when the vehicle is left unattended.