AC units for buildings are usually size so that there is a 20 degrees of cooling from the ambient temperature. With an RV the problem can be that the AC units are not sized correctly or have too short a cycle time. It takes time to remove the moisture from the air and cool down the interior spaces and sometimes a lower BTU rated unit that runs "continuously" works better than a high BTU AC.
Most RV's are built for "3-season" use and so not insulated for temperatures below freezing and so also not going to be great when temperatures are over 100 degrees. The advantage of an RV is that it can be moved to where the outside temperatures are warmer or cooler.
I grew up without air conditioning in my houses or my cars and trucks and it was not something that bothered me all that much. Friends with homes in the desert did not have AC either. Now AC is considered a necessity in the USA and so we use more electricity and add more to global warming which is not a good cycle to be in for us or for future generations.
If one is planning to spend months in the desert then building a structure to provide shade is worth considering. I see this often with trailers in areas where there is a snow load to worry about and the similar protection could be provided against solar loads.
On a more immediate basis if you can locate the RV so the rear is to the south then there will be less wall area exposed directly to the sun and having the side with the awning facing southwest would also help, if you have an awning.
