Thank you for your post.
The Wall Surface Tool allows up to three layers to be added and since there are three layers that you need I would recommend using this.
If you create a material for each of the skins (battens will need to be shown as a skin and not a gap, but can be disregarded in the takeoff) you should get a result similar to the image below. This way the end result will be the correct thickness.
Would you be able to please let me know if this works for you?
- Wall Surface Tool - Adding Layers To Walls (Curtom).png (2.5 KiB) Viewed 3133 times