So last night I stepped back and took a look at the project overall, and was not really happy with the main structure. It was rather misshapen, and was getting too bulky and heavy. So I removed the instant cave off of it and took the main structure apart, keeping the original cave in tact. Meh, this is my first rock formation, so I'll allow myself some mistakes and re-dos. Boy just a little of that silicone is really quite strong. I used an X-Acto knife to cut it apart. I may need to use a wire brush to clean up old silicone.
So now, repurposed the original smaller cave (because it had a floor), and attached it to the two instant caves that I just created a couple of days ago. It's not quite "back to the drawing board" but it is back to a very basic foundation.
Honestly, I may just keep it simple and not build it up too much more. I may add a few more rocks in the corners to round it all up and make it look like a unit.