I use Celluclay for my ground work, so any fences or walls are put into that before it dries. Hopefully you can see what i mean here.
![](http://i246.photobucket.com/albums/gg111/Bish_012/251-3%20Ausf%20D/2014_12160007_zps71b5b50b.jpg)
On this one, the fences posts are sunk into the 'ground' with the fence slat stuck to it, just as on the real thing.
![](http://i246.photobucket.com/albums/gg111/Bish_012/Su-85/014_zps723677ae.jpg)
I am a bit confused as to what you are planning on using as a base. It sounds like it will be thin and not very strong. What are you useing for ground work.