Well... i'm not too sure whether Egg crate foam did wonders, but i have it in my install. Unfortunately, i did it along with the RAAMmat-ting of my front doors. Of course, there is difference before and after the install, but i did it together... so... not too sure if the egg crate brings any wonders but the before and after sound of deadening + egg crate is fuller sounding(after of coz) than before.
And i didn't use any moisture barrier on my egg crates, they don't seem to give me any problem, even after nearly half a year, they didn't grow any fungus.