Shade as has been mentioned numerous times and if possible a second roof AC unit even if a very small one.
If you only have a 30 amp feed for the trailer your roof AC will draw 18-22 amps on start up and drop to 12-16 when running. a small 8000 btu unit like the coleman mach 8 cub draws about 12 on startup and then runs at about 8. You would be maxing out with those two running, no microwave, coffeepot, or other high amp uses would be possible but you should be able to get a second unit to work that way, and if your most common use is going to be summer desert, you may want to explore better windows at some point.
If you dont mind the aesthetics, you could use suspended cieling tiles to some areas on the interior, at least they would provide a finished surface appearance with the ability to glue strips over the joints.
Good luck
