Structural Foam for chassis stiffening

I will be interested to see how this thread goes. I too have been concerned about the use of foam in these old Mopars. I never heard of it being done and when I saw it I thought it would retain moisture. I just bought a 68 Dart that had new quarters installed a decade ago and was then put in storage. Who ever did the body work, filled the space between the outer quarters and the trunk floor extensions with foam. Everyone tells me I've got to get all that foam out of there or it will rust away as soon as its exposed to moisture. I fear that it may be the only thing holding the bottom of the quarters in place and if I eliminate the foam, then the whole car will need to be redone right away (which is not in the budget).