I use a rubber mat (one side has rubber and one side has indoor outdoor carpet) and it kind of bridges the gap over the center keel. I can lay a plastic tackle box on the floor in front of me and it stays there without sliding around as well as anything else I lay there. It's not permanent so doesn't add any weight to the kayak for loading and unloading.
That foam shouldn't be any issue as far as adding weight, and it does take care of the noise and slippery deck.
Just one more cast!