Structural Foam for chassis stiffening

This is just my 2 cents and someone else might have already made the statements but...i didn t read this whole thing. I work on cars at the bodyshop everyday. Been seeing a lot of pickups with foam in the wheelwells on the bedsides rustin out right where the foam is. As far as structural foam goes..look at the 2009-now rams. Rockers are completely filled with it and the rockers are so far the worst spot for rust on them. Ruating from the inside out just like thebedsides. Holding moisture is what i m getting at.
On the other hand. If u can properly treat the metal on the backsides of these areas...i think its a great idea
Catch 22