I don't mean this to be flippant, but when I get too hot in my camper, I go outside and sit at the picnic table. After a few minutes out there, I have a whole new appreciation for the temperature inside.
I just got back from a 10 day trip in Texas. There were some really hot days. On the last leg of my trip, I duct-taped some aluminum foil over that cloudy window in the door. I could not believe how much that dropped the temperature! I wish I had thought of it sooner.
I also put the vent pillows in, run a box fan on high, keep the blinds closed during the sunny hours, use the awning to shade that side of the trailer, and keep the bathroom door closed as much as possible.