If you are parked in direct sun, it will be hot. To relieve some of the heat, try opening up the roof vents (heat rises). It will still only be 10-20 degrees cooler, but that is something.
When we were in Phoenix last year, it was 113 degrees. We had no shade but there was a breeze. It felt cooler outside under the awning with the breeze than it did in the rig. So we opened the windows on the breeze side and cranked up the A/C. Got the temps inside down to about 85 while the sun was still high overhead.
If you can find shade from the afternoon sun, do it.