The University of Texas Amateur Radio Club, N5XU, has an AM-6155 ampifier on 222 MHz. It is a rack-mounted amplifier with an Eimac 8930 tube that puts out 400 watts on 222 MHz. Airflow is from the front of the amplifier, through the body, and out the back. The rack is pushed up into a corner (there is literally no other place to put it) with about 9" clearance from the wall bhind it. The amplifier actually sticks out of the back of the rack a little bit, so there's only about 6" of clearance between the back of the amp and the wall.
As this was an FAA ground-to-air unit before being converted to Amateur service, I imagine that the amplifier was just put in a separate room where nobody cared about the fan noise. The fan noise is very loud and objectionable, though, and especially so in a small radio shack of less than 100 sq. ft. Are there any common tricks to reducing fan noise?