In a remote mountain hut we have three external doors. Having had many breakins over the years (two involving attempts to burn the building down, one of them completely successful) we want to make the rebuilt building more secure. The external doors are made from 18mm tongue and groove timber with a frame around. I intend reinforcing the edges of the doors with angle iron. I'd like to reinforce the doors more by attaching plywood on the inside so that it's harder to smash through the door. Each door would need two panels about 800mm X 600mm, and I guess somewhere between 10mm and 15mm thick ply.
What's the best way of attaching the plywood? I was thinking of sanding the paint off the interior of the door and using some kind of wood glue. I could also use coach bolts with the head on the outside, but that may be overkill.
Here's the inside of a door