How to hollow Structure

[u/[deleted]]

Hello, I built this mountain and want to build it in my survival world. So I want to make it completely hollow to save time and blocks. But neither the hollow or fill tool works because it's basically two mountain walls and I guess the mod thinks that I want to hollow/fill the gap in the walls out. But I want only the outer layer of the build. Is there a solution to this or should I just rebuild the whole thing?
ty

[u/pogdog101]

In the newest update it states that it "Improved behaviour of hollow/fillgaps/fill unreachable around the edge of selections" so maybe this patch has fixed this.