It wasn't clear exactly what Wagner was looking for.  Fiberglass/epoxy
is put on styrofoam "cores" quite routinely in many fields (for example,
this is how most surfboards are made, as far as I know.)  If a chemical
coating won't work by itself, you might want to use something like a
lightweight fiberglass cloth to serve as a matrix for the resin. (other
types of cloth would probably work as well.)

BillW