Try putting some java moss on your wood. Fluff it up a bit so extends all the way from the wood to the surface. I don't bother to tie mine, it kind of roots itself after a few days. It grows like a weed and the firebellies LOVE it. It can support their weight so it makes a good lounging spot. They are pretty much in there all the time.
My avatar is even a picture of one of them in the moss