Hi
I build a raft like this once, it was same size as a standard plywood
sheet that covered top and bottom and around the 4 edges I made a frame
in very heavy timber. It was the best small work platform ever. It's
still floating 20 years after but take my advise ; make a heavy
frame,rough dovetail corners ,this not the styrofoam is what make it
work for years. If you compromise and don't make a heavy frame the
thing will last only a few years .
That raft was btw very popular ,small but not to small ,handy and
rugid. ----