the associated window is permitted as best illustrated in fig3 through 6 and with concurrent reference to fig1 and 2 it can be shown that the upper grate assembly 12 comprises an upper plate 18 securable across an upper portion of the window 14 by a plurality of threaded fasteners rivets or other conventionally known fastening means a medial plate 20 of similar construction relative to the upper plate 18 extends across a medial portion of the window 14 and is similarly secured thereto by a further plurality of threaded fasteners or the like the upper grate assembly 12 further comprises a plurality of receiving tubes 22 which are fixedly secured to both the upper plate 18 and the medial plate 20 and arranged in a substantially parallel spaced relationship relative to one another preferably the receiving tubes 22 are positioned along an interior surface of the upper plate 18 and the medial plate 20 so as to be positioned between the plates and the associated window 14 however it is within the intent and purview of the present invention to fixedly secure the receiving tubes 22 to the exterior of the plates 18 20 if so desired with continuing reference to fig1 through 6 it can be shown that the lower grate assembly 16 comprises a lower plate 24 of substantially similar.