slots indicated generically as 196 the placement of plate 24 in this position may tend to enclose internal air cooling plenum 26 plenum 26 may then have an inlet indicated generally as air intake 36 at array 196 and an outlet indicated generally as 200 at the upper laterally offset end of the enclosure an outlet array 202 may be mounted across outlet 200 between a retaining guide or channel 204 mounted in the roof portion and an angle retainer 206 installed along the lower edge of array 202 and secured at either end to shoulders 82 84 outlet array 202 may be in the nature of a flow resistance element 208 that may be porous in one embodiment array 202 may include a large number of tubes or a honeycomb or honeycomb like structure see enlarged detail of fig1 b that may tend to yield a measure of flow resistance and that may tend also to cause the flow leaving the plenum to have a relatively flat velocity profile that is the velocity of cooled air leaving the plenum may tend to be generally uniform across the outlet array or more uniform than it might otherwise be the resulting plenum structure may be thought.