I don't know if it will help, but I found on Siege I didn't need a double wall, the inner wall could be just half height, and as such not visible. Though of course it does mean you can't place anything in that area. That was when players could cast nature's fury through the walls. Not sure if the same applies to casting dark wisps.
I've used knee walls like tables. You can place an object, raise it with the design tool, then put in the knee wall. The items have to be raised a certain number of tics to be above the wall, or they will go to the moving crate with a redign (sometimes when you add the wall, sometimes on the next one).
Sometimes you can just drop items right on top of some knee walls. I think it's something they coded in, but never got it to work right.
In effect, you can make a ledge. It's static though, you can't just drop things onto it like a table. Stuck in the design you make.
Pegasus statues work great on them, for a decorative style. I would think certain furniture would be cool, but might be risky for storage in this case.
