Plenty of small AC units at lowes, you just have to pipe out the hot air they produce, and a third part monitoring device to monitor the Temps.
If I can make one suggestion, k9s have cars especially built for this, with monitors, auto roll down windows, alarms and pagers. One failed the other day and we lost a good boi.. point is, for traveling this is ok, but never ever leave the truck because systems fail, fuses pop, ACs overheat and shut down and heat strokes happen fast.
<----- avid dog lover. Good on you for keeping them comfortable.