Someone removed the grey foam thing- now what?

I just scored a 1999 model Wave Sport Forplay. The only issue with it is someone in its previous life hacked through the grey thing in the bow, compromising the integrity. How can I repair this? The foam support runs under the seat. The pics show the piece that was removed and then the inside foam hacked to pieces.

Gray thing alert!!!

Order some closed cell foam or similar buoyant material on-line(I once cut up old life vests),get some Weldwood contact cement(use in a well ventilated area)and go at manufacturing a “new” one…In the meantime, shove a bow float bag in there(Won’t prevent a cave-in if you get pinned, but it’ll keep things afloat. >:)