I would like to add some additional flotation to a new ( to me ) boat that I
purchased. Does anyone know if any of the brands of canister foam ( Great
Stuff or Dow etc. ) are closed cell and could I use them safely without
concern that they will take on water over the years.

Or, for that matter, could I just use blocks of Styrofoam? The application
is "outdoors" ( on the permanent step/trim tab) on the boat. I'm just trying
to give her more flotation at rest.

Thanks, RichG