Our RV awning looked terrible -- leaf imprints, grime, dirt and what looked like mildew. I used a homemade, car-cleaning mixture, and it cleaned everything without a lot of scrubbing; the awning looks new. The recipe comes from Reader's Digest 13 Weird Things to Clean Your Car:
Pour 1/4 cup baking soda into a gallon-sized jug, then add 1/4 cup dishwashing liquid and enough water to fill the jug almost to the top. Screw on the cap, shake well and pour 1 cup of the mixture into a 2-gallon water pail. Fill the pail with warm water, stir to mix, and go to town. Good luck.