A differential pressure monitoring apparatus includes a case having a continuous sidewall including a first end closed a by first end cap, and a second end closed by a second end cap. A differential pressure monitoring unit mounted in the case includes a differential pressure sensor in communication with the external environment, a temperature and humidity sensor in communication with an internal atmosphere inside the case, a data processor operatively connected to the sensors, data storage, an information display viewable through the case, a non-gas permeable membrane tube in connection with the differential pressure sensor and an internal environment and a harsh and/or corrosive gas filter in connection to the differential pressure sensor.