Structural Foam for chassis stiffening

The only issue I would have with respect to any kind of foam in a street car is water/moisture absorption. In a race car it wouldn't matter so much but I live in a very corrosive and humid environment. I would never put anything in the frame or in any part that would be exposed to water (rain). It would be a death nail for my rust free Barracuda. But in some areas of the US you don't have to worry about that???
JMO
Treblig