One of my friend has converted his FORD F-250 to CNG (compressed natural gas) and keep telling me how much cheaper it is. In my area the price per gallon equivalent of CNG is only $2.79 while the gas(premium) cost $3.99. Anyone has done the conversion for their X5? Please post your experience here. Is it hard to do?(My friend sent his F-250 to a shop to do the conversion, but that shop doesn't do BMW). I know the cargo space in X5 is tiny and a CNG tank will take quite a bit of that space.