Most company's will want to see a gas safe safety installation certificate type of thing , unless you explain exactly what you are using it for and how it works most think you are like a plumber and just carrying a cylinder in the van not using it for a portable shower unit that's mounted in the van , again you MUST HAVE AN EXTERNAL EXAHUST TO CARRY FUMES OUTOF THE VAN , leaving the rear doors open isn't sufficient ventilation , this is all basic stuff just ask a gas safe installer they would not be allowed to fit it or Evan work on it unless it's fitted in this way , Ime in the fire service and have been out to a number of properties that people have been poisoned and some have Evan died as a result , it's just a matter of time before it happens to someone in a vehicle , don't risk your life just for cheap hot water get it fitted properly and safely