I use an Ryobi electric pressure washer with a Ryobi foaming soap canister at the end of the wand on my 5th wheel. I use a foaming Car soap I bought at Wal-Mart as the Ryobi soap gets to be expensive. I coat the area I want to wash with the soap and then let it sit for awhile. This really helps on the front cap to help soften the bug guts there. I then use a long handle car brush that reaches all the way up. Then set the soap canister to water only and rinse. 5th wheel comes out looking great and never a high pressure that if used incorrectly could damage the decals etc.
I use this on my car, truck, lawn tractor and 5th wheel. The big benefit is dirty soap water never gets put on the vehicle.
Dave