Can I suggest that you start with a sankey rather than a penman? I know they are older but by all accounts from people I know in the military they are better. They are also cheaper, and most importantly you can get spares for them (a lot of parts are common to series land rovers), whereas the spares availability for a penman is limited even in the military. (last story I heard was about having to machine from scratch a hub bearing collar as you cannot get a replacement and the military option was to fit a complete new axle). Also the main issue with a sankey is the tub rusting which can be repaired easily enough but if you are doing a camper conversion is probably not needed anyway!