My best solution for you is go grab the thickest dishwashing detergent in walmart, I had good experience with Fairy liquid in the past but they never make that kind no more.
1. Clean your car.
2. Pour the detergent on the areas you would like to protect. (Be generous)
3. Spread around with your hand.
Thats it. Leave it on until you get to your destination then wash everything off.
Everyone used to do that when traveling across the desert in Dubai and Saudia. We used to cover the whole car tho except for windows ofcourse due to sand storms there.