When I removed my quarter from my 71 Chevelle there was 2 places that had like a foam filler or sponge filler between. These were on the sail panel and outer wheelhouse. They were in bad shape and I cannot used them again.

What could I use here to take up this gap? Spray foam, expanding foam? Some kind of caulking? I take it they are for vibration and extra support to prevent oil canning.

I know there have been a lot of quarters replaced by some of you. What did you use for the vibration pad?

Any help would be appreciated

I think that the stuff is there to keep the quarter from collapsing if someone leans on it. It's a pretty big, flat area that needs a little support. Anything that won't hold moisture will do. I used a tube of silicone on our '72 Lemans Sport.