Can you fill the bottom of a boat with styrofoam?
Of course you can, because Styrofoam can float on top of water
for a long time. A lot of newer boats have Styrofoam in the bottom
for added buoyancy if you do add it to your boat, be sure that
there is no moisture in the bottom of boat when you do it if not
completely dry , moisture will be trapped and eventually rot any
wood that was used in the boat's construction.