I have the same tree stump as you, do your FBTs ever go inside of it? I was debating whether or not to use it in my setup because i was wondering if they would get stuck... did you fill it with rocks or something?
There is one female that goes inside of it from underneath. When I saw her in there the first time I was freaked out because I thought she was stuck, but she climbed right out of the top at dinnertime!! She is REALLY fat too, but she was that way when I got her.