I have two 12" Geek Aire fans and a 9" Opolar fan. Both types use rechargeable lithium ion batteries.
The Opolar fan leaves a lot to be desired as compared to the Geek Aire fans, which are sleek, powerful, and well-constructed. But the Opolar fan is lightweight and moves (some) air. If I wanted to, I could probably hang it in my stock trailer easily. It has a high and low setting. On high, it only lasts maybe 3 hours max? On low, it will last about 7-8 hours… but low is very low speed. Like, you can’t feel any air if you are more than a foot away from the fan. The fact that it’s a USB fan may be a perk for traveling; while I haven’t tried this, you could probably charge it in the truck. It does take quite a few hours to charge.
The Geek Aire fans are just fabulous and superior in every way. But in my stock trailer, I couldn’t figure out a good way to hang them because they are heavy and pretty large. I have been bringing them with me on trips and just setting them on the floor when we are parked. Maybe one of their smaller models would work better in a stock trailer?