I have had good luck with one of these rechargeable fans clipped to the grab handle in front of a screened window when sleeping in the car.My first step to over landing... But really just at a close campground. First time sleeping in a vehicle. Have the ADGU SS1 with sleeper platform, an Exped Megamat XL, window screens, Jackery 1000 powering an Iceco JP42 and phones.
First night was a little rough. It was way too hot out for me, but would have been the same in a tent. I hit my legs on the sides and feet on the Tailgate.
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Amazon product ASIN B08C74XV6S
Also, tailgate open with some mosquito netting over the opening helps a lot.