Be VERY VERY careful using a power washer-- very easy to bend the fins.
Please confirm, but I believe your cooling system is STACKED (vs sandwiched).
So it is only a single layer thick (CAC usually on top of radiator).
Since I believe your OE cooling package is Aluminum, you need an aluminum friendly detergent. Best is probably Simple Green EXTREME-- designed for cleaning aluminum airplanes.
Since it is a single layer thick, you can do most of the cleaning from the back (back of coach). With radiator cool or almost cool, wet down the metal (garden hose with regular garden nozzle). Use a spray bottle to apply detergent. Let it sit for a few minutes, but NOT long enough to dry out. Systematically rinse down from the top with the hose nozzle. Repeat until nothing dirty comes out.
Probably wouldn't hurt to put plastic bags over things in the engine room you don't want wet, like the alternator.