If making a watchtower from scratch is a little above your modeling skills, you might be interested in these very nice paper model watchtowers.
Making Group Movement Bases
Here’s a illustration of how to make some very nice looking group movement bases.
Making A Wicker Fence
Barking Irons has a tutorial on making an english style wicker fence.
How To Make A Maori Pa
Here’s the beginnings of a tutorial series on making a Maori Pa.