Say hello to your best friend for terrain gap filling - joint compound.
This stuff is great for working with scenery. If you have a gap or need some texture, just slap a handful (or less) of this stuff on it and you are good to go.
The best part is the more you buy the cheaper it is! You can buy a little tiny can of it for a few bucks, or a quite larger can of it for a few bucks. I was almost tempted to get five gallons of it because it would have been CRAZY cheap per/unit compared to the smaller sizes but my wife did not think it was a good idea.
So remember, next time you have some terrain that isn't going to hot, just try a bit of this on it. If all else fails just say it is possessed or was made by Orks. That's what I do!