I brew with a few friends, and we are up to 3 fermentation cabinets (6, 8, and 10 carboy capacity). We only need to keep the wort warm since we brew ales and mostly in the cooler months in the basement. Just a basic plywood box with 1" pink foam insulation, a 110 volt thermostat and a couple light bulbs in the aluminum housings from clip on light fixtures. Not sure what to do if you live in a warmer climate or brew lagers.