I have used the JayBobBoy method, tying duffel bags with clothes, bedding, tent, 25x25 Aluminet to the roof between the bars, sometimes topped with a bike or two lying flat. Even 20' 1" PVC pipe curved to the front bumper for a monkey hut, though that is probably asking to be pulled over and is easily available in Reno. Theoretically someone could steal it all if you park somewhere overnight or eat out of sight of the car. That's why I like Dragonpilot's idea. Hard shell ones would be more aerodynamic, but more expensive. I would imagine car top carriers are widely available on Craigslist.
Inside vehicle goes water, picked up at the last minute, camp tools, rebar, personal items. I'm down to 3 large duffels, which are waterproof nylon canvas =<8000 cubic inches each, bike, knapsack and water.
Have a great roadtrip, sounds like fun!
increasing the signal to noise ratio with compassion