that little truck still has quite the following!...

https://www.luvtruck.com/ownreg_full_pic.php

Variation on a theme is to have a few towels.
Soak all in water wring out and put in freezer.
Remove from freezer wrap in dry towel and place around neck.
When the formerly wet towel dries out replace with another from the freezer stock and put the original towel back in the freezer after another soaking.

Works well but you need another towel about every two hours or so at 40 C so a decent supply is required if you have more than one person.

Pete.

My great grandfather used to hang a sheet outside the biggest family room window in their farmhouse. He rigged up a drip system to keep the sheet moist all day and voila, he had himself a swamp cooler. Apparently it was pretty effective for what it was too.