Door at the front of the enclosure.
Vents at each end of the enclosure. I like to have one vent down low (on one side of the enclosure) and the other up high (on the other side of the enclosure), the high vent lets hot air out (because hot air rises) and the lower vent sucks in cooler air (because when the hot air leaves through the top vent, it pulls in cooler air from the lower vent)