How thick is the skin according to your estimates and figures?
Well, you can make an estimate of the outer hull for yourself...
I never thought about much being housed in the corridor-walls. Wouldn't that be a problem if a high intensity phaser-blast hits them?
As opposed to the floor or ceiling?
The only high intensity phaser-blast
hitting a wall in the series was when Scott was attempting to cut his way into engineering... and he expressed just how delicate the work was.