BTW, don't seal up the rock sides so much that you cannot get some water movement around the eggcrate structure. Also, might be useful to drop a few bits of PVC under there for fish to sleep in a night.
You can't see from the pictures, but theres a square hole in the very top of the hill to drop in a small powerhead or two for some circulation under it. With that being said, would you still suggest not foaming up to the glass?