I transport my dogs for work, used to use an estate car with seats folded and two big solid cages, windows down, at work I could mostly leave all windows and doors open and I was rarely more than a few yards away from them. Only real problem was sitting in slow moving queues on motorway, and the spaniel dust and hair blowing about.
Now use an ex police dog van that I had a big bit in designing the cages. Got a forced air scoop on the roof feeding direct into the cages and void above it. The cages are insulated from the sides, and stay nice and cool, a white van helps massively too. The rearmost side windows have been removed and have twin electric fans in each side feeding directly into the cages. The air con can also be switched into the rear, got temp sensors in the cages too.[working out how to add gsm pager to that] And a ventlock to leave rear door ajar. Emergency contact stickers all over the place.
Usual caveats apply, just don’t leave dogs locked in car, when its warm. I’m never far from them at work but still take a massive amount of care to ensure their welfare.