Deck lid rattles bigtime

It sounds like a tin can being kicked down a cobble stone road. The problem is the globs of body filler the factory sandwiched between the inner and outer skins has all fallen out over the years.

What have you done to fix yours?

I'm thinking about using a long skinny tube (like the clear plastic one on the refrigerator ice machine) and squirt some Great Stuff expanding foam up in there. The tube fits nicely onto the nozzle provided with the can of foam. I could guide it into place through the hinge mounting hole by taping it to a stiff wire. I also have the holes that were cut for the go-wing mounting brackets.

Anybody see potential problems with using that foam? Is it susceptible to retaining moisture and causing rust from within? Something has to be done, I can't tell you how annoying it is.

Jerry