Please everyone, if you wax your rv's or any of your vehicles, do not use dish soap. It will strip the wax off the first time you use it. Use any car washing soap available at any auto store, Wal Mart, K Mart, ect ect. Dish soap will clean, but strip the wax and over a period of time dull the finish.
I've been detailing my cars, including Corvette's and Mustang's (show winners)for many, many years, and would attack anyone that came within 50 feet of my cars with dish washing liquid.
Go to Auto Geek.com. Plenty of good info and tips. Its geared toward vehicles, but would apply to rv's also.
As for your pressure washer, no way!!! May be good on your truck, but an rv has so many seams, openings, inlets and outlets that you'd run the risk of blowing water in.
Grumpy