Here is a nice 12 volt cab fan for summer.

[Waterloo]

I have had this same fan for around three years, it works like a champ and really moves the air in the cab. The open blade design makes it easy to keep clean, just dust it off. The blades are a soft plastic, so when you forget it is on and get to close, it will not hurt you. I have mine mounted, hanging from my upper console over the dash, it does swivel, side to side and up and down, so you can direct where it blows. I rarely turn it off, and it is great when it is time to sleep, as it really keeps the air circulating in the cab. It has two speeds, hi and low. Low is fine, as high is just a bit too much.

https://www.amazon.com/gp/product/B00NYT...uage=en_US