Ok guys, coming from my 30 years of owning a mobile pressure washing operation let me give you some advice. I have pressure washed thousands of trailers from tin sides to million dollar motorhomes. If your pressure washer comes with a O degree tip, THROW IT AWAY. If you don't know how to use a 15 degree tip or a rotator tip then THROW THOSE AWAY TOO. Always use a 40 or 60 degree tip. Stay away from close contact and keep moving. We use a hot water 3000 psi unit with 2 guns and 5 gals. per minute. Put soap on with low pressure, bottom to top, brush scrub, and rinse top to bottom with hot wax injected into rinse water. Never had an insurance claim in 30 years. As mentioned above dirt or film requires scrubbing to be perfect.