1) Look for shade to park under
2) Use your awning to provide shade on your passenger side
3) Use Reflectix to insulate your windows
4) Block off sections of your motorhome to shrink the area cooled by your A/C system. If possible, block off the front cab area completely using blankets since a tremendous amount of heat will come in through all the windows.
5) If you can feel a lot of heat coming down through the ceiling vents it might be better to block those off with vent pillows.
6) Plan for meals that do not use appliances: The microwave will compete with the A/C, and the stove top will just add extra heat into the space. Think "Sandwiches and Salads,