what to use between the fender and inner fenders?

I'm getting to the point of mounting my fenders on my 71 cuda. was wondering what people like to use between the fender and the inner fenders?
It seems the factory stuff was a foam, shot out of a caulking gun. apparently it came out faster than the workers needed it to. I've seen some real messes with that stuff.

SEM 39357 (flexible expanding foam) or 3M (similar product)

Both make a correct appearing product when applied and painted.

Warning: mount fenders first, then "add" the expanding foam between the panels. The working time for these products is too fast to apply it in the same manor as the factory did.

Yikes ... 15 second work time . Not even enough time for it to seep down between the panels !!

Not if you have two people, but you better be ready. LOL

I did mine this way and it looks perfect

I just removed my A-body fenders today for paint/body work, and was also wondering if anything should be reapplied to that junction...

I am not concerned about correct appearance, only about future rust, so could I use brushable seam sealer instead?