While it is certainly conformable, and pretty strong, it doesn't weigh much, and wouldn't make good ballast. It would strengthen the hull much, though, and could be a good choice (depending on how it reacts to water, of course) as replacement for the sodden foam you are removing.
so many options....
lucky me I have quite some time to think on it before I need to decide
I wonder how an underfloor, foam embedded water tank would work?
Water is pretty heavy. Centerlined it'd act as ballast. When trailering (out of the water) less weight is a plus...drain the tanks.
Superlative!