Abstract: A retainer assembly can be clamped to a support crossbasr, such as is provided by a vehicle roof rack, and is able to retain an elongated member, such as an extension ladder, on the roof rack without the use of tools, clamps, tie-downs, etc. Each retainer assembly has a vertically-extending body, a transversely-extending part and a downwardly-extending retainer portion forming a retainer hook, the transversely-extending part being enclosed in a resilient sleeve. The ladder edge is inserted under the retainer hook while in an elevated attitude and then rotated downwards so that the edge rises up in the hook and compresses the sleeve, whereupon the ladder is held securely by the compressed sleeve between the retainer hooks and the cross-bars. The procedure is reversed to remove the object. The transversely extending part is adjustable vertically along the body, and the retainer portion is adjustable horizontally to accommodate ladders, etc. of different cross-sectional sizes.