This may help.
I recently cut to the shape to fit the inside of all my rear windows of my 80 series windows with silver sun shade that is used for windscreens.
To my amazement, it has made a huge difference in temperature. You can buy this off the roll at clark rubber. It's slightly different, silver lined 4mm black foam but it works.
The other thing is you need some sort of hot air scape on your roof. I'm thinking of something like our Jayco roof vent.
Having said that, there are some nights in the Jayco when there is no breeze, this is when we need some sort of 12v cooler.
Ive had a thought about a 12v fan with a wet cheese cloth hanging in front of the fan...............yep, you have to soak the cloth often.