We've gone through a few models... this one actually seems to keep us cool (along with open vents on the tent walls):
Badass fan (needs 8 D batteries--will last a week on low setting if you run it 8-10hrs a night) https://www.amazon.com/O2COOL-Battery-Operated-Adapter-Graphite/dp/B00ATSHJ1Q/ref=mp_s_a_1_1_sspa?crid=1QJQUG30MY0KK&keywords=o2+cool+10+inch+battery+or+electric+portable+fan&qid=1553025255&s=gateway&sprefix=o2+cool+&sr=8-1-spell-spons&psc=1
Cheers mate!