No manufacturer allows for a sealed enclosure system. They have specifics for clearance for natural airflow, but then operation must still be within manufacturer specifications.
The proper way to deal with airflow is to draw air (with fans) from the bottom of the cabinet and then exhaust it out of the top of the cabinet. A cabinet typically will have a bit of an overhang on the front edge near the base, this is the perfect location to put slots in for air intake.
At the back of the cabinet, near the top, you will have to have something similar which can exhaust the hot air from.
Middle Atlantic, as well as several other companies, make fans which can pull airflow through the cabinet to ensure that your gear is properly cooled.
You may also want to consider getting some pull out/rotating equipment racks if you aren't planning to have any natural rear access to the cabinetry.
It should be very much under your consideration: If you have any ability, whatsoever, to open the back of the cabinet up in some way, then you might want to build something to allow for that. Rear access to gear is one of the best things you can do to service the gear, enhance reliability, and provide ventilation. Often people say that they can't do it, but then they don't really think about the fact that they aren't going into an outside wall, but a wall that may lead to a different room and it very well could be done very nicely.
In my time in residential, there is no question that the #1 killer of A/V gear was heat build up due to poorly designed custom cabinetry. I've seen dozens of pieces go down due to this.
