Grace and I have a Field workshop soon and apparently people work out of their cars (with appropriate precautions, including fans). I may still be the a-hole who runs the A/C. Kinda freaked out.
I would take precautions and plan not to use the AC no matter how hot it is honestly. You might very well in a trial or match setting get asked not to come back. Lot of trials we do everything from the car - doesn't mean your dog has to be in the car. I drive a sedan and put crates behind my car with blankets as shade, water buckets in crates. You can take extra water to use to wet a towel repeatedly like soak it to be in the crate to lay on.
If you do this more often you may want a shade cloth either the aluminet to drape over a car with a hatch or over a shade tent to keep it cooler and the other goodies people take, but for a one day or part day thing just use common sense while packing.
That must be a horrifying childhood memory
We were so careful while on vacation last year to leave an adult with the car at all times as we had to take the dogs everywhere we went. So an adult would sit in the car with the hatch and doors open if hot, often by the trees at the edge of parking lots. I got asked more than once if I required help. It was nice, people seemed to care more because we had dogs with us.