Abstract: A motor vehicle, such as a semi-trailer or the like, has an elongated load-supporting horizontal base frame having a first and a second end portion. A plurality of supporting legs are mounted on the base and pivotable between an upright orientation in which they engage the ground and a substantially horizontal upper retrated orientation. Mounting arrangements mount these legs on the base frame so that they can be shifted transversely of the elongation thereof underneath of the base frame, and laterally outwardly thereof, respectively. A vehicle-mountable chassis frame also has a first end portion and a second end portion; the latter slides under the cooperating first end portion of the base frame when the chassis frame is moved lengthwise beneath the base frame in order to support the latter when the legs are in the retracted position thereof. Guide ramps are provided on one or both of the cooperating end portions of the two frames, to facilitate the movement of the chassis frame underneath the base frame.