With a coolmist running 24/7 it is usually overkill for a fruiting chamber in terms of humidity.
I suggests to have it on a timer set for 1-4 mins on and 5-10 mins off. Keep in mind that this will depend on your ambient temps, and space of your boxes.
the humidifier is only for humidity, not for fresh air exchange. Your polyfill holes will have to match the water evap rate of your setup.
too small of a hole will cause moisture buildup and subsequently cause your mushroom pins to abort and stop growing.
too big of a hole and there will be no humidity. you will need play around with your hole size. your evaporation rate will have to match your humidity rate.
2 key things are fresh air exchange and 95% relative humidity. without these 2 things constantly mushrooms will not fruit.
I suggest buying a analog hygrometer at any smoke shop or cigar shop. And calibrate them by covering them with a damp towel. after 1 hr, turn the dials to 100%. Analog hygrometers are only accurate within +or- 20% of what you calibrate them at.
digital hygrometers are notoriously inaccurate and cannot operate all all ranges.
Calibrate your chambers to have 95% RH and drill more holes as needed. Remember to wait 1 hr between measurings to get a accurate reading.
Theres some really good info on shroomery on fruiting chambers. search keywords terrarium, fruiting chamber, martha, shotgun FC. Find ones to suit your needs, those guys there will set you straight.
for the visual learner, theres good videos on
http://www.mushroomvideos.com/ to get you started.