Thread: Lining a safe

Looking to line a large safe that @40mm put in for me over the weekend. It's painted steel on the inside walls and floor. It's an 800kg thumper of a combo fire/security safe, so would be very temperature stable.

I've seen some synthetic stuff sticking to and marring blued finishes, and would like to avoid that.. Had considered marine carpet/astroturf/lino or similar glued to the floor and walls, but I'm nervous for steel buttplates, muzzles resting against the walls etc. Also untreated thin timber paneling came to mind, pros and cons of that?

Any other options to consider?