Abstract: An adjustable frame for carrying vehicles between elongate upright sides includes, on each side, a forward end and a rearward end, each end including an upper and lower rail section joined by elongate brace members, where the respective ends are separated from one another and a length-adjusting insert is carried between such ends to selectively permit adjustment of the position of the forward end relative to the rearward end while maintaining the ends in end-to-end alignment. On each side of the frame, preferably at least one of the upper rail sections has an end portion defining an open-ended hollow tube extending lengthwise of that side within which an elongate arm of the length-adjusting insert is slidably moveable so that structures on the outside surfaces of the rail sections will not interfere with length adjustment.