Have you guys actually looked at the heft of the CMC body sub-frame members?
2" X 3" X 1/4" thick Box frame members with a cross frame member (the Napoleon Hat) 12" in front of the tunnel opening.
I'm not particularly worried about pan flexing.
Besides..... It's a 3"H X 6" W opening with the rest of the tunnel intact (and that tunnel is only 1/16" thick sheet metal). I would expect to see a small ripple or crease in the tunnel near that opening by now, like when I had the carpet out to re-do the seats. I saw nothing and an OCD engineer would see something like that.