How fa$$$t do want to go?
Hey John. The body shop supervisor told me that the foam acted as a structural support between the lower quarter panel and body frame. The same method that is used (by some manufacturers) between the front bumper cover and actual steel bumper plate. He showed me a piece of block foam (looked like standard packing foam) that FORD uses in the front end of some of their models.The pre-15 models rusted because the foam prevented moisture escape out the drain holes. Many repairs done by body shops have had significant amounts of water pour out when drilling in from underneath or cutting into the panel from outside to make discovery on how far rust has migrated. On my 2013, I pulled out the rear seat and dug out all the foam and dissolved the rest with acetone. Then after a good neutral chemical flush, we dried with compressed air and sprayed the shit out of the entire cavity on both sides with Fluid Film. Just recently on my son's 2018 Hellcat, we did the same when brand new with the fluid film. At one point in the past we tried to contact the Brampton assembly plant to ask why they filled these areas with foam but, we never got an answer.