Chassis stiffening through foam injection

[NickBW]

I believe ford uses foam in on certain spots on a few vehicles such as navagators and expedition and IIRC some BMW's make use of it as well.

Few of my concerns:
1)Although I've heard the foam(or at least the brand I looked into) has stuff in it that prevents corrosion I'd be worried about blocking drain holes. I've seen this come up a few times in the miata/mx5 camp.
2)I have "heard" with out any real confirmed proof, that many of these structural foams can or will break down with in a handfull of years. I'd love to see this confirm or denied though.
3)I've heard of some foams(great stuff ??) expand too much and can actually damage the chassis.
4)Perhaps not so much as a mark against using a foam, but a warning. Make sure the chassis is perfectly square before applying. I would assume this is easier said then done givin the fact that our cars have lived thru twenty years of life, bumpy roads, moisture and a few bangs here and there and they never were the most rugged chassis's on the block.