Be careful if doing this for washing as it can get very slippery when wet!
For windshield, sunvisor and nose cap cleaning/scrubbing I usually do the following...
Open the hood, step up on the passenger side step then onto the tire, over to the frame and then up the side of the engine to stand on the valve covers(don't worry they are fairly thick aluminum, I am 285lbs and do this all the time) and radiator mounting braces, just don't stand on the fiberglass cowl below the windshield.
If I were power polishing the stainless steel nose of the box (which I have been meaning to do for a couple of years now) I would be tempted to build or rent/borrow some type of scaffolding for the extra stability.
2007 Haulmark 3329DS, Freightliner Coronado Chassis, 515hp Detroit, Meritor Freedomline 12speed Autoshift, 10kw Generator, In-motion Satellite.