The stuff Gandolfi is using is not what your thinking of, it is marine grade MDF, it don't expand, contract or strip out, a good sheet of marine grade MDF will cost you more that a piece of Good quality Birch Plywood, if I remember right the last time I looked at some 1/2 inch marine grade, a 4x8 sheet was around $250.00 US, there are many different grades of MDF, what we normally are exposed to in the states is a very cheap product, you can take a piece of marine grade from a good manufacture and put it under water for 6 months and it won't change at all, it will stay the same size, stay flat and still be usuable..perception is a big thing in woods, but believe me this stuff makes solid wood look like junk..
Dave