T@B 320 Factory Photos Showing Locations of Items Before Hidden in Walls

I love all of the pics posted. It's definitely fascinating and helpful. Does anyone have any pics to add of what the inside of the exterior walls look like? A fellow T@Bber cut a porthole window into the side of his T@B and I wanted to do the same. It's only 10" so it shouldn't compromise anything but I've read where some have been told they affected structure with a screw in the frame. Here's a couple of his pics. It appears there's some metal or metallic tape within the walls. Is there a diagram of where this is and whether or not anyone can tell me if this needs to be avoided?

I know there are many bathrooms that already come with a much larger porthole window and I've seen where people have had their T@Bs cut and the bathroom window installed after market so I think it's ok to do but I'd like to know about that metal in the wall before I cut anything. TIA