Cave in!

We've started playing the Underway campaign (battle reports to follow). As we discovered at the start of the first game it's possible for part of the ceiling of the caves to fall in and crush your troops, leaving a big pile of rubble behind.
So I set to work making a cave in marker.
One old CD, some circles of polystyrene ceiling tile and an assortment of rock chips later...

I then added some sand to fill the gaps a bit and add a bit more texture.

If it stops raining for more than five minutes I'll hopefully get this sprayed later today.