Do a recon to know where to park remembering that the sun moves all day. Be sure if possible to be in the shade in the afternoon. Insulate your van, particularly the ceiling. Wear light cotton clothing. Sprinkle water on your clothing and the fan will evaporate the water cooling you.
Canvas shoes seem to be best in hot weather.
Have as ventilated seat or fold a wool blanket over 4 or 5 times and make a seat cover out of it. Strange as it may seem it will feel cool.