The left-seated pilot stated that she was recently hired with the operator and was new to flying survey operations. The right-seated pilot was training her for survey operations. They filed a flight plan for a 5-hour survey flight and filled the fuel tanks full. After takeoff, the fuel selector was set to the outboard tanks and after 1 hour and 50 minutes, the inboard tanks were selected. After another 2 hours and 20 minutes, the pilot noticed lower-than-expected fuel on the gauges and opted to end the flight early. Approximately 10 minutes after turning back, the engines had intermittent power loss and were sputtering due to low fuel. The pilot made a request to land at a nearby Naval Base and declared an emergency. The controller communicated runway 14L was closed. The pilot approached runway 14R and noticed people and objects on the runway. They were redirected to land on another runway, but the airplane was too low and touched down on grass. The airplane continued the landing roll into a security fence, damaging the fuselage and both wings. The pilot reported there were no pre-impact mechanical malfunctions or failures that precluded normal operation.