Dan,
I still think you'll get away with your car if you wash it on Saturday morning. Trust me, when you get to RIR, it'll get dusty from all the dirt that floats around in the air. Our cars were layered with fine sand dust and I had to constantly use my california duster to get rid of it all.
BTW, when do you plan on leaving? We can caravan together...you know I'm right off of 270.