Yours is a unibody car right? The body structure carries all the weight that used to be carried by the frame rails in older cars?

I wouldn't count on the foam as forming a useful 'structural component' although it might do well enough filling those voids and helping to make your car look a little better.

If you have large enough holes (!) in your car you should have no problem with using the little srpay cans to squirt foam in there as a stop-gap measure to get a little more life out of the old girl. DON'T mix up a five-gallon bucket of the goop and pour it in there without having enough space for the excess to escape.

Regardless, plan on dong a real repair in the not-too-distant future. All you really need is some sheet steel and some pop rivets, which you could finish off with body filler. The metal would help support the weight of your car so there's be less chance of leaving a large chunk of it (the car!) somewhere on the Parkway.

Good Luck! Steve