An adjustable retainer for attaching a receptacle, such as a thermal cooler, to a vehicle includes a frame for securing to a vehicle, such as a truck bed. Opposing jaws are movable in guide slots in the frame. One jaw may be manually positioned in a guide slot having hooks, while the other jaw is movable by a linear actuator secured to the frame. The jaws allow optimum positioning of the receptacle and create a vice-like retaining mechanism.