I am dredging this up for discussionsince I am working on the very project for my rework of the Scamp
I have not decided how to go about installing the thing yet, On the outside is the only way I can see it done, but I am considering making a front flange of the face that can be mounted through the wall in the front in the shower area.
The front will be accessable from inside, but all of the combustion and fittings on the outside. A bezel to match the wall and a this SS sheet metal box on the outside to weatherproof it and allow combustion air in and the flue will have a 4" chimney cap to keep water out.
This will be a SS box on the front in the center of where it front window was before I filled it in with a fiberglass panel.