Carmen

I just used what I had on hand and spaced it out a bit. I think it mainly dampens the sheet metal so it doesn't reverberate like a drum if something hits it. You can see where the factory applied various zigzag cut pieces along the back walls for similar reasons to dampen vibrations.

I can't say yet.  I've got a couple of more days to still terminate everything and get it going.  Still need to mount an amplifier under the seat and a small subwoofer.  It's turned into more of a project than I initially planned but I intend to use the van for several years for touring with a travel trailer while retired and thought this will be worth while.