How to fill hull solid without overexpansion damage

[sbklf]

I filled the hull with foam blocks and some pour foam to fill voids pre sole installation because I did not want to overexpand and put stress or damage the sole and the hull. I will sand and cut the high spots now hoping to get it as close to the bottom of the sole as possible but I am sure I will have some voids. I can glue the sole down first then drill holes in it and fill it with resin like they did before but dont like this because it adds a lot of weigtht. I was thinking about drilling small holes and pumping non expansive material in to fill the voids.

Any suggestions on what to fill this small area with to make it more solid.