Here is what I do and it takes the temp down almost 20 degrees and I do NOT run the coach AC.
If your windows are not tinted put up removable limo tint for the summer time.
Covering all the roof vents with those RV roof vent pillows.
Pull Shades all down and slip van windshield sun shades under them.
Covering your skylight with removable limo tint.
Those plastic not air tight roof vents let in a ton of heat and I have three of them. Just putting the pillow covers in 'them' made a big difference. And second in line was covering that gaping skylight letting the heat in.
Do all of the above AND turn the coach AC on and your passengers will love you for it because now the AC can keep up and it really gets nice and cool.