Which of the following is essential for securing the stability of a cargo tank vehicle?

Chock blocks are fundamental for securing the stability of a cargo tank vehicle by preventing it from rolling during loading and unloading procedures. These blocks are placed against the wheels of the vehicle to create a barrier that immobilizes the vehicle. This is particularly important when dealing with liquid cargo, such as propane, as any unintended movement could result in spills, leaks, or accidents.

Using chock blocks maintains the vehicle in a stationary position, ensuring that operators can perform their tasks safely without the risk of the vehicle rolling away. Moreover, this safety measure complies with regulations aimed at protecting workers and the public from hazardous situations that may arise from unstable cargo tank vehicles. In this context, the other options focus on different safety aspects or securing items within the vehicle rather than addressing the direct stability of the vehicle itself during operations.