We've been using one of these 9" usb fans all Summer long and highly recommend it.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
It's whisper quiet, extremely portable and sips power. They are a fantastic way to increase airflow especially down stairs on warm nights. Two speed fan... put it on low and you can hardly hear it running. Easily powered from house power or from a portable phone charging battery out under the awning. We had the small 12v reciprocating fan that came with the van but it was way too noisy for me. This has made sleeping during Summer camping a lot more comfortable. They make a 6" as well.
No affiliation.
Joe