I continued my work on the ventilation system. The temperature was awful. Several times I found myself struggling and dripping with sweat. The following photos best describe how it was all completed. There is no fan installed as yet but that will come next time. That's why I have two CPU fans.
As usual, my workbench was the sandy ground. I completed cutting out the vent hole with a jigsaw. Then I cut the vent hole for the next vent. I did use my vent caps. If I get water ingress then I'll resolve that by putting aluminum tape as a roof over the tops of the vents.
I didn't install the second vent because I don't have any more 4 inch vent caps. Mind, by that time, I was just about ready to collapse on the ground from the heat! If the heat extraction does not work brilliantly then stage 2 will be my planned heat exchanger.