I accidentally posted in the Class B section so I am starting a new one here.
My motorhome has been sitting for a couple years as I was out of state. When I got back I had a nightmare of a clean-up to do.
I have tried multiple products on the exterior. The ones that seem to work best are Bar Keepers Friend followed by TSP or oven cleaner.
In any case it has required scrubbing with a stiff bristled plastic brush to make any progress.
My pressure washer broke a couple years ago but it never really did much good unless the surface was pretty clean to begin with.
Another thing is, It sits on a farm right now, with a well. I have to be careful with how much water I use 'cause the whole farm can run out of water. Pressure washing is a no-no this time of year.
The coach is in pretty good condition aside from the exterior looking like it's been at the bottom of a lake.
My back condition(s) aren't up to scrubbing the entire thing efficiently.
I have some pix to show what I've done and what I'm up against.
Door
Scrubbed with BKF and TSP then partially coated with Zep (shiny area)
The worst side. Getting the green stuff off is easy. It's the dirt that is in-bedded in the grooves that I'm working on (see door pic above).