We wrestled with that too. By the time we finished with the tank the bridge and 3D background would have been too much. A deeper tank would have probably made that possible because you can set a sparse foreground to lead up to the background.
I know this was years and years ago, but i found this thread looking for a swamp themed tank and trying to get ideas for mine. I wanted to say if you're still around, the shack looks awesome and gives me so many new ideas for my setup!