i'd start with two or three roof vent fans. Powered by solar-maybe 400 watts plus depending on what else you're using. Four deep cycle batteries would be good again depending on other loads.
These fans allow you to open windows where you are and create a stiff breeze and quickly evacuate the heat-enough that interior temps will essentially be like outside in the shade.
I'd still want to park under a tree to minimize fan usage and allow the power to be used to recharge batteries from night before.
Locate solar panels in the sun.
For backup or extremely hot days, a quiet generator from Honda or Yamaha.
Some of this can be adjusted depending on how long you'll be at the site.
