[FT] Terraforming Styrofoam

I discovered a new Art Supply store yesterday, and I picked up some
items
for making FT terrain -- two wooden balls (about 1/2" in diameter), a
strofoam ball (3" in diameter) and a strofoam hemisphere (8" in
diameter).
The plan is to turn the hemisphere into a gas giant, and the smaller
items
into moons -- all grossly out of scale with the ships, but they should
look
neat.

Here's the question of the hour: how do I seal this styrofoam?	It has a
very rough texture; not beaded, but very porous.  I'm thinking of using
miliput, which is very easy to work with when you have enough water, and
adds strength besides.	I'm not sure if this is the best option, though.
Anyone done this before?  And if so, what'd you use?

John X Crimmins
johncrim@voicenet.com
  "...is one of the secret masters of the world: a librarian.
They control information.  Don't ever piss one off."
  --Spider Robinson, The Callahan Touch.