I talked with a service rep and was told that nvh would work as an anti-flutter materiel, but they did not know if it had adhesive strength to pull the frame upward. I hope that the gap is just from it drying out/ rotting out. Also check the bows the support the roof and anywhere else that might use this. This stuff is good to use if you have trunk rattle from a big bass system. The only thing is it is not cheap, and is around 80$ is the cheapest I could find. Most of that cost is for the gun to apply the product. I would see If a local body shop has a gun you can use.
Note: 3m sells two kinds of this foam I don't know and could not get an answer if 1 was better then the other or was stronger. http://3mcollision.com/3m-flexible-foam-08463.html
I been searching all day and found 20 different answers but the over whelming thing was don't use panel adhesive or urethane glues. The foam has the proper flex and wont ripple the sheet metal. I'm not sure if it is strong enough to pull a sagging frame up or pull a bowing hood skin down. I do know it is used on the door panels on my Saturn to prevent rattles from the plastic skins and it stuck them on pretty good.