I ran mine with recirc air passing back into charger, didn't cause any washing of the charger on the over run, but a very minimal amount of corrosion occured in the pass-though on rocker cover, but nothing in charger, as most of the surfaces are greased or coated.
I'd reckonmend placing nozzle between the intercooler and the throttle body for best results. I also had a second nozzle/atomiser mounted on the bumper spraying in the air flow directly infront of intercooler. It didn't reduce my charge tempereature any further, but it made it drop down faster.
Back when I ran this setup I achieve my boost temperture at the same as the ambient air temperature, which was effectively an 11 degree drop compared to not having it running. 21 deg C @ 17psi.
Think I did a post on the old PSD forum at the time, but its gotta be at least 3/4 years ago.