That's a great location for the heater. Be aware of the fuel pump noise traveling down through your swingout.
If I decided to rebuild the window insert I would fabricate it horizontally and put it on the second row window
instead of the 3rd row window.
Depends on the controller you get. My first one I was able to adjust the temp and the air flow. I set it 20 celcius with minimum air flow. This one I have now I am not able to set the temperature so I can only set the airflow to minimum.
I've had several of these that I bought from Amazon or ebay. It's a crapshoot of what you get. The Vevor you posted is better for stability on the ground.
Don't have high expectations. If it works you are ahead of the game already. When they work they work pretty good. When they don't work, keep...