As far as Las Vegas in July "hot" doesn't quite cover it. It will likely be something north of 110 and could be significantly higher. Expect your RV to get down no lower than 90 if you are lucky. We live just outside of Tucson so we're familiar with "hot".
Hopefully your frig is on the same side as your awning and the winds are low enough to deploy it {not always the case}. Try and get a site with some sort of shade that might be available but there's not much to be found in most of the LV parks. Won a contest once and scored 3 free July days in Vegas... second prize was ten days. :B