In this photo, the ghost wood was siliconed into position and some aquarium silicone was spread where the foam was to be sprayed. The terrarium was then left for 48 hours to allow the silicone to cure, and then Handi-foam (a brand of spray foam meant for ponds and aquariums) was sprayed around it to make a 3D surface onto which to silicone background material. It's not very easy to see but in the upper left, the foam protrudes quite significantly forward - I did this so I could carve a "shelf" there. The foam was also used to seal gaps around and behind the wood, so frogs can't get trapped. The foam was allowed 4 or 5 days for a crude cure.
