Well, there's definately another mantis haunting my tank
I can hear him excavating away in the rock and managed to catch a glimpse of him a couple days ago. He was in a rock that isn't easily moved, but I haven't seen him since. I think I'm going to try a DIY bottle trap this weekend and see if I can't get him out.
Another bit of good news, adding the second batch of rock (which was fully curred) did wonders to reducing the smell in the house. We don't even notice it anymore unless the cabinet doors to the sump are open. I've also noticed a lot of condensation in my canopy. The back is open, but the condensation problem seems to be up near the front. I'm hoping that the canopy is designed for the humidity and well sealed. Maybe it will be better once the lights are on and there's more heat in there?