I got to work one of these afternoons. I cut a hex-ish shaped piece out of the large chunk I got, using the baseplate as a rough template. It wasn't as simple as I thought because that foam is quite thick. The main goodness is that it's a lot sturdier than normal styrofoam and doesn't crumble as awfully.
The whole piece was quite thick compared to the scale of the model so I cut off about a third of it, with the idea of making the cut very irregular. That irregularity was to make it more natural looking. Of course it doesn't look much at this point:
So I impaled that thin piece to the proof-of-concept piece (that rectangular MDF-plate with a metal wire going through it) and sprayed the whole thing flat gray. It'll need some fixing still, but it's a start. It's also nice that I can work on the balcony with these things better now that the sun stays up for a bit later so I don't have to struggle with the little light that comes from the living room windows... ain't the approaching spring just awesome?
Next I am going to cover the top parts in thinned down white glue and then dump a load of sand on it. And then, I thought, I'd spray that again with the gray thing. I believe it'd be quite space-y. In case it doesn't go as I think it should, I can still repaint it until it ends up how I want it.
I'm just hoping that the gray base wouldn't make the whole view way too gray with the darkish metallic Imperial X-Wing. We'll find out soon enough.