I know this may sound silly.... so forgive me if it does....
But one of the things I think about is shrinkage- which I have see in some old styrofoam.
My experience is that if the styrofoam is tight- like in the well cars, then I guess all is OK.
But when it is NOT tight, and the car can move around a little, abrasion can happen.
That's why I really like that stuff (don't even know what it's called) that Kato and Atlas have been using for the last 20 years or so.
I have some of the models in Styrofoam packaging from the 80's and even earlier and earlier and I have not noticed any shrinkage. If it was tight, it still is tight. And in most cases it starts off pretty tightly cradling the model. Styrofoam is a pretty stable material based on Polystyrene. The one used in the model packaging is also denser (less air) than the stuff used for insulation or terraforming on layouts.
I tried to Google for mentions of shrinking Styrofoam but all I found is silly experiments. But that search did bring up a valid point. Since Styrofoam contains lots of air. it will shrink when heated (plastic melts into air-free solid) and also when under air pressure (the air bubbles get compressed). But I don't see how that would play into packaging stored in human-habitable air pressures and temperatures.
