Can be variable. We were at Canyonlands NP in June, went hiking before noon, huddled in the shade in the afternoons; it usually cooled off in the evening but takes a while because of the heat in the rocks. I recall a couple of hot nights and one really bad sand/windstorm.
Try to position your trailer so it's in the shade in the afternoon.
Also might dry an evaporative cooler with a small fan if lots of water is available. The air's so dry there, water easily evaporates and cools down the surroundings. Maybe just a bunch of towels soaked in water and hung up would help.