Abstract: A telescoping trailer cover assembly has a stationary section (16) and three movable sections (17, 18, 19) coupled in series. The three movable sections (17, 18, 19) are supported on wheels (38) having V-shaped grooves (39) for running along respective tracks (31, 32, 33) having a projecting V-profile. Cam rollers (41) are mounted near the wheels (38) and are positioned to run underneath the tracks (31, 32, 33). A drive system includes a pair of endless loop drive chains (66, 70), which are connected to the rearmost section (19) of the cover assembly (10), with each chain (66, 70) running longitudinally down a respective side of trailer (11). The chains (66, 70) are driven through sprockets (67) mounted on a common drive shaft (55), which in turn is driven by a pneumatic motor (50) through a gear reduction box (51), and a further gear reduction is provided by a pair of drive sprockets (52, 54).