Fantastic Fan makes a 12v fan that I believe is called the Fantastic Breeze? I bought one after a lot of research and I can tell you it moves a lot of air. With it and my Fantastic Vent Fan running in the trailer there is a noticeable air movement from one end to the other. It has three speeds but I don't usually go above one, two gets a little noisy and three is just too much air for me.
If I'm correct it draws 5amps an hour so if you ran three fans for 8 hours you'd be drawing 120amps in a night. Not sure what your battery situation is but you'll drain a standard battery quickly with that load.
1999 Suburban 2500 4x4, 2016 Jayflight 23RB Elite, Fiberglass, Polar Package