I know some people prefer a freestanding strongroom, so it can be observed from all round. That one seems to be ideal from that point of view.

Actually talking of mud walls...... I once put a small SR in a location where the existing walls were adobe. They really were all over the place- corners were not square, walls ran off straight and vertical. So we put the block work in as specified- the blocks with 2 hollow squares in them, and then filled the hollows with a special mix. We had plenty of mix and so suggested filling the void between the adobe and the blockwork. It was anything from almost nothing up to 6" in places. The job was much better for it as the hole would have been a rat run.

Normally I would never pour concrete against an existing wall as the wall would almost inevitably crack, but there is so much give in adobe that this wasn't a problem.

As I sit here musing I just wonder what anybody thinks on existing walls. I was always told never to "use" an existing wall, or floor for that matter, but to build a wall to specification inside the existing. Of course it all depends what the customer orders.