LPG will still produce carbon monoxide , I would recommend using a detector in your van ,and ventilating it well. It is propane really just the same as what is in the red bottles on thousands of caravans, the new ones have really strict regulations as to the safe use and operation.
I would go down the LPG route , it is very safe and much cleaner than diesel , so long as you have ,and stick to proper procedures and common sense .