Open-cathode polymer electrolyte fuel cell (PEFC) stacks use hydrogen as a fuel, are a high efficiency power source, and do not produce CO₂, NOₓ, SOₓ, or particulate matter. When used as a remote power source, the PEFC stack must be protected from adverse environmental conditions. To provide optimal operating conditions to the PEFC stack, an actively controlled enclosure is proposed. A mathematical model of a transient, non-isothermal, lumped parameter, open-cathode fuel cell stack is developed and coupled with an enclosure model. The open-cathode fuel cell stack mathematical model includes characterization of the cathode channel, the anode channel and the membrane electrode assembly (MEA). The transient mass and energy transport equations for the coupled system are solved to determine the optimal operating conditions for the PEFC stack within the enclosure. A Horizon H-12 Fuel Cell stack and two enclosure designs are tested, characterized and fitted to the mathematical model.