Trucks maybe captured, or destroyed, if unaccompanied by friendly combat unit (squad, halftrack, tank/SPG) by any enemy combat unit which moves into the hex. The enemy unit, may continue to move through the hex. Destroyed trucks are removed from the hex., while captured truck is replaced with a truck model from capturing players side, which may then be given an action, if desired, and moved away, in the same action phase. This rule prevents the tactic of trying to block hexes with trucks only.
It's simplest to just treat trucks as equipment that doesn't require a squad to operate.