I am going through that same learning curve myself Tim, I used sheeting on top and bottom on the Green Impact, but a different aproach. The blue foam is of course insulation foam, Home depot, or Lowes or pretty much any building supply company of worth will have it. THe thing I didnt like about the floral foam is that its fairly fragile and can compress easily ( at least the floral foam I have is) but the blue foam seems to be problematic in that its rather plastic, malleable , and doesnt cut well with sandpaper,, though I did just get a couple sheets of long board 36 grit and I will find out if that works better to rough it out,
anyway, not trying to hijack yoru thread, just sharing..
good luck,, and pick the right grain balsa for molding, learned that one the hard way too.. sigh