Background installation:
This ended up being a little trickier than I had anticipated. I couldn't wrangle the big piece in with the glass in place, so I had to cut it into two pieces.
Used pond foam to fill in the gaps and secure the driftwood.
First time I'm using this product and I like it much better than Great Stuff because of the color. I don't have a picture before carving, but after carved it already looks a bit like pumice rock.