You could just make a cube editable_ select two opposite sides_inner extrude_select the two extruded polygons_Use the bridge tool across these polygons( you may have to turm on the Xray option in the Display menu)_select all the sides without holes in and hold down the period key and left grag_make a few knife cuts close to the top and bottom of the hole to tighten up the edges.
If in doubt scream and shout.