New life for an old scow: styrene insulation foam; trex pl..

Am thinking of breathing new life into an 18' flat bottom scow byusing some
materials I had lying around: adding 2" of styrene insulation foam to the
outside of the bottom boxed in with a trex kelson and chines, then screwing
on 1/2" plywood bottom and 12" strake sides to the trex, and finally
glassing and expoxying the new bottom and sides. Done right, the trex and
foam would never see water (encased as it would be by ply and epoxy), and
the hull would float 2 1/2" higher (less any displacement for the new
weight). Should have the effect of making the existing hull self-bailing.
Anyone have any comments or experience with the above method or materials?
Thanks!

Dick