Possible Clues:

• Keep carrying box
• Sidney Box?
• Box for the 9 across of your vehicle
• Container for the weight of an automobile with another vehicle on it
• Continue to haul container
• The weight of the vehicle is in the container
• What the vehicle weighs, just in case (6)
• Focus on heavyweight boxer's piece of kit?
• When the motor is 25 down, that's the weight of it
• Dickensian hero appearing in the box