While it can be dangerous preparedness is what matters. I've lived in a desert that reaches 115 degrees in summer my entire life. It's not a place you'd visit from somewhere more temperate but it is survivable, even without AC. So-called dry heat is far easier to deal with. The afternoons after a major thunderstorm are typically the worst of all worlds. Generally, if you avoid staying in the sun, stay hydrated, and seek shelter from around 11am to 4pm it's not so bad. Peak badness occurs between 2-4pm in my region.
That's not to say its _easy_ and without AC it can be uncomfortable. But you can survive. If you have an RV, fans, perhaps a make shift swamp cooler, and tin foil on the windows could get the internal temp down below 80 pretty easily.
Generally speaking anything over 100 degrees can be dangerous to the under prepared. At 110 degrees direct sun exposure can be lethal if you are not drinking approx. a quart of water per hour of exposure. But it _all_ comes down to exposure. Shelter changes the entire game.