To each their own
That said, during July and August, going to one of the hottest places on earth is probably one of the least forgiving places on earth. Common sense (which I'm certain you have) dictates you have plenty of gas and water, and I would only stay on paved roads. Biggest concern would be cell phone service in case of bad luck and you break down. End of the day, rental vehicles are generally driven like wanna be NASCAR drivers who figure it's not their vehicle, so if they "beat it up a little" driving, who cares? Needless to say, daily tire and fluid checks would be mandatory IMO. Someplace like that area I'd really rather be with a local and know all the in's and out's of the area.
Funny, I took some rental SUV's from Vegas where I probably shouldn't have gone in Utah. Seems like the rental companies are catching on.
This is a dumb general question to those who live out in the area. If I stay with a minimum 1/2 tank of gas and always refill at that point, would I be ok? I know whenever I drove out west to paddle or flew out west to hike , I would always have at least 5 gallons of spare gas with me. I never needed it on all my visits adhering to that half tank rule, and I assume if I adhere to this rule I should be fine.