If we're talking only the hard sides, then you can go either way but washing like a car works well. For truly stubborn stains, I've had to use L.A.'s Totally Awesome slightly diluted or even full strength.
And waxing it is always a good thing.
If it's the canvas and vinyl parts that also need a wash, there are a number of products out there but the one I use is the Camco Full Timer's Choice Awning Wash from Walmart. It's fine for a general cleaning of the fabrics.