The understructure provides a flat platform sub-assembly suitable for building up into all body types. It is of welded unitary type having inverted top-hat-section side rails and box section cross-members and longitudinals. The cross-members extended outwards from the longitudinals to carry the lower side sills. The front end assembly comprises a one-piece front lower panel to which is welded the one-piece windscreen aperture panel. The toeboard is welded to this structure and runs back to the front wheel arches. Two inspection covers are provided in the toeboard panel for brake and clutch hydraulic system servicing. The quickly removable engine cover is hinged at the front and retained at the rear by two toggle type fasteners. Rubber sealing gaskets are fitted to both upper and lower engine covers.