Electronic Freight Security (EFS) systems are being increasingly deployed to reliably monitor the cargo in real-time and prevent theft in air cargo. As the existing technologies fall short in achieving these goals due to cost of deployment and/or higher latencies, we propose to exploit the existing infrastructure of power lines when the aircraft is on the tarmac. We propose an architecture that extends power line communications with Bluetooth Low Energy (BLE) devices that are embedded on the cargo. We show that BLE mesh can extend the range by interfacing with PLC modems to achieve an IoT solution for continuous monitoring and tracking. In order to evaluate this, we also propose a novel software-defined radio based testbed that can be used to evaluate various scenarios. The novelty of our testbed includes BLE mesh network that supports high reliability and low latency communication and support for emulation of electrical loads to inject impulse noise into the powerline network. We then measure end-to-end latencies and packet delivery ratios in realistic settings for the smart cargo monitoring solution. Our results indicate that our hybrid network offers a worst case latency of 24.85ms for a 570 m distance between warehouse and cargo monitoring station.