pass through window use?

We used it for our cats. They could travel with us or decide they wanted peace and quiet. The most important reason has already been mentioned. When it is very cold or very hot outside, the pass through window done a lot to achieve a reasonable temperature in the camper. Also I like to leave the doors open for visibility. The sliding glass on the truck has a very dark tint. I have a Fresnel lens on the back of the camper and like to watch the traffic behind me.