I am not so sure about it being a dumb idea. It appears to be injected into refrigerators. I have seen it used in refer and freezers on ships - course those were stainless steel.
I do not underetand why it would be a rust magnet any more than any other unventilated space - assuming you leave no voids.
The big caution in my mind would be when the stuff swells. Shipyard had a big problem with this factor. Built large forms like those used in concrete. I can easily see it warping a cab if hi expansion was just willy nilly shot in and no allowance made for expansion.
Dan Bentler
