Perhaps it's time to remind everybody about 12v A/C units. They use water, with or without ice, and the ones using a heater core for the heat exchanger work in any humidity, and actually dehumidify the air.
I fired mine up today for the first time this year, in anticipation of the coming heat wave. I used only water, no ice. 95f outside, and I shut the van up on purpose and parked in the sun. 115f inside when I turned on the A/C. 30 minutes, it was down to 75f, and at 45 minutes down to 65f, when I shut it down and went back and parked in the shade.
I really didn't need it today, because I was fine in the shade with my windows open and a fan, but I wanted to test it before I needed it, just in case.
These A/C units are pretty cheap and easy to make, one of the local news channels even posted directions on how to build a simpler version for I think they said $18, cooler and all. If the heat is going to bother you, you really need to build one right away.
I saw a different design of an ice powered cooler last week, that is simpler and shouldn't add any humidity too. Only power needed is for a 12v fan. It was kind of the typical 12v ice cooler idea, except they put the ice in a sealed container. I can't tell you how good they work for sure, but a pet rescue in FL made a bunch of them for their pet transport vehicles to keep the pets comfortable.
You're going to be running a fan anyway, so that design wouldn't use one bit more power.
Stay Cool out there my friends!