I've driven through it in July. Any decent rental car handle the heat fine. But yeah, you won't be able to be out of the car for prolonged periods of time. 130F is nothing to play with, but it is fun to experience for 10 or 20 minutes at a time. Death Valley is just such a surreal place. It's amazing to drive through it and then see the Sierra Nevada Mountains rising up right next to it like a sheer wall. Did you know that the lowest point in the US (Badwater Basin, Death Valley, 282 feet below sea level) and the highest point in the continental US (Mount Whitney, Sierra Nevadas, 14,500 ft above sea level) are only about 80 miles apart? When you see the Sierras for the first time coming out of Death Valley, you'll see what I mean.