Just a quick FYI on the chicken tunnels before I finish catching up - I lost a bird to a bobcat in one. It pounced on the tunnel & tore the birds head off but couldn't get the body out. We caught it on it's 2nd try. So, with that said I really liked my tunnel but I can't imagine how I'd make one safe enough to have here again. Just a thought...
I am fortunate to have (unused) metal ducts laying around in the garage. I often thought about laying it down, and using it as a support/hiding spot in the tunnels. It’s all short enough that it should not build up too much heat/condensation.