Transporting cylinders in cars, vans, or in any enclosed vehicle is extremely dangerous, and should be avoided. Never transport flammable gases in the trunk or passenger compartment of a vehicle. Many persons disregard this warning every year, and there are many vehicle explosions as a result. We urge you to have the cylinders delivered in an appropriate vehicle.
LINK..
http://www.airgas.com/content/details.aspx?id=7000000000010
I don't use gas myself. Is it not extremely dangerous to have your boilers fitted to rear door's though? What would happen if you had a hard impact from the rear and sparks hit a ruptured pipe or joint on the unit. Would that be kaboom or am I missing summat?
Quote from flogas website about transporting gas in closed vans,
Carriage in Closed Vehicles
Flogas do not recommend the use of closed vehicles (such as vans) for transporting LPG cylinders.
If LPG cylinders are to be transported in closed vehicles the following requirements and restrictions should be applied:
If a MAXIMUM OF FOUR cylinders are to be transported:
Cylinders should be loaded in a single layer and secured to prevent movement;
The cylinders must be upright, with the valve at the top (the outlet connection should be fitted with a blanking cap or plug;
Flammable gas danger warning diamonds should be displayed on both sides and the rear of the vehicle;
If MORE THAN FOUR cylinders are to be transported:
All of the above apply and in addition;
The load compartment must have vents at the front and rear (or positions recommended by the vehicle manufacturer) to give a flow of air through the load compartment. The rear ventilation openings should be as low as possible and the total area of the ventilation (divided equally between the front and rear vents) must be a minimum of 2% of the area of the load compartment floor.
The maximum recommended net quantity of LPG (in cylinders) carried in a closed vehicle should not exceed 200 kg's.
Gas tight plugs must be fitted to all cylinder valves that do not have a secondary means of closure (FLT type cylinders have a secondary means of closure).
Cylinders should not remain in the vehicle whilst stationary for more than 2 hours, unless the ventilation is improved by opening all the load compartment doors etc.
If there is a smell of gas;
Do not move the vehicle until the source of the leakage has been found and the vehicle has been declared safe by a competent person.
Increase the load compartment ventilation by fully opening all doors and vents.
Do not turn on any electrical equipment.
The regulations governing the transport of dangerous goods vary according to what dangerous goods are being transported, how much is being transported and the gross weight of the vehicle.
http://www.flogas.co.uk/142/transport-of-lpg-cylinders