Hi there,
I'm not sure about the hook up to trip computer/range etc but,I am getting an mpg reading off the computer.
Remember though you also have your petrol tank to put petrol in.
The system starts on petrol and at a predetermined engine temp changes over to lpg automatically, if you run out of lpg it automatically switches back to petrol.
Service intervals on the computer ,as far as I know ,are unaffected ,but as a gas is burnt and not a petrol vapour oil service can be doubled mileage wise and spark plug life is also doubled (not sure if I fancy changing plugs every 150,000 miles though) but it does give an idea how efficient it is.
Lez