Ok I hav sliding door n to workshop sheeted with cladding on to 40mm box. Goin to silicon bond sheets to box then pop rivet so as harder to remove sheets to gain access. Was thinking of 9mm ply riveted to inside of box an stuff ‘cavity’ between it an sheeting wit sheep’s wool. My thinking is if scum try to use grinder to cut way n wool will jam blade an slow there way in. And add some insulation to door also. I presume wool isn corrosive?