Backing you up on the temperature variations- Hubby and I were there in 2010, ending our trip Memorial Day weekend. At Bright Angel Campground, we saw the thermometer hit 120 F. I had to break the ice in a pot of water left out overnight on the South Rim...

One thing that really helped us was some space blankets. I used them to shade our tent and the ground in the canyon, even as a make-shift shelter when we were told (with other hikers) to wait out the sun before continuing down. Even the ground stayed hot until well past Midnight unless I had the spot shaded with a space blanket.

Have a blast!