Decided to go with some pink foam strips. I had a small piece kicking around and it was much easier to form into shape than wood.
Here is the gap before:
I dry fit foam along the gap.
Mixed a somewhat thin batch of PB so it could run into all of the gaps, also added some 1/4" chopped fiberglass.
I filled the bottom of the gap with a pretty thick layer of PB. Then I smushed the foam into the PB making sure it gushed around all of the edges. Not sure if this was the best way to fix this area, but at least its done. This another one of those spots that I spent more time thinking about how to fix it than actually working on it.
Thanks for all of the suggestions and advice.