Looking good 
Will the base colour of the base be different from the asteroid's base colour?
And what about the range of those laser turrets, are they able to cover all the approaches? 
I'm thinking either a dark grey for the asteroid and white for the base, or a grey-brown for the asteroid and a contrasting grey -black for the base.
The guns still move in the mountings. The elevation can change and they can swivel 360 degrees, though I'm sure they would have limiters fitted to stop them hitting the base. The three gun's arcs overlap too.
I'm urging the filler to dry as I want to see the paint go on! 
Thanks Steve. I still need to decide on colours.