Below is the finished project. Now I just need to wait 48 hours before rinsing and adding to my tank.
I sort of took the long way around to this project.
Lessons learned: Don't plan a large rock-work project using small stones. It just does not look right. However, I bet with larger stones, and a larger container, this method could be used to make larger formations. However, I'm not sure how well the silicone will work with heavier stones. It sure does work well with lighter stones. Strong and flexible at the same time.