Houseboat

[Ray]

If it is saltwater, please don't use metal drums. Dat's bad.
It all depends on the bouyancy and density of the foam.
And it can't be open cell foam, it will absorb the water and sink lower in the water.
I see people using those white styrofoam floats used for laying pipelines across marshes. Not sure where they get them from. They hold a lot of weight.

If I were you, I'd try to find an old party barge. Replace any rotten plywood decks and paint the pontoons with a barrier paint. It will probably last longer and be cheaper.
There gots to be one somewhere that someone is wanting to get rid of cause of rotten floors and/or burnt up motor. The toons and framing are all aluminum. Should last a long time.