The problem with bondoing on to the back of syrofoam is that the styrene in
Bondo attacks the foam also although not to the extent that resin would.  
Still it will tend to distort the surface.  Also, Bondo doesn't release well
even when well waxed.  Lastly, you would have to bondo the whole thing.  
Bondo is a LOT harder than foam and sanding cuts down the foam very fast
while leaving the bondo standing out, even when sanding with a block.  Green
foam used for flower arranging is not affected by styrene and could be used
also but that stuff is real garbage.  Divinycell is expensive and harder to
get but is unaffected by styrene so that may be more viable but it is harder
to shape.  Anyway, if you are goig to use styrofoam, it is a lot better to
tape over it or Saran wrap it than to Bondo or dissolve out the stuff.

Dan Newland

ES #61