Epoxy wont attack polystryene or pool noodles (foamed polyethelene or similar)

Polyester and vinyl ester will attack polystryene foams, but not the expanding or surf board foams.
Surf board foams or similar core materials tend to be heavy compared to stryene or pool noodles.
The best is a sealed container fill with air.
What ever you choose must still be sealed to reduce the absorbtion of water and fuel.