Hi, I have a 2002 auto Frontera SE and it had 41000 km on the clock when we bought it. I put it on LPG at 50000 km, and I have done 160000 km to date. It has run very well on LPG. As good as petrol - no difference. It is very economical to run and it has been a great car.
Unfortunately the auto trans is now playing up and I have to decide whether to fix it or move the car on. When we got the LPG installed, we went with a direct injection system, which was perfect and cost around 4000 with a 2000 govt rebate. This type of system was the only system suited for Fronteras.
Re the last comment, we did exactly what you intend to do 7 years ago whilst our auto 02 Frontera was near new. I have driven this vehicle with injected gas towing a bobcat on trailer a few times, an overloaded caravan from Melb to mid QLD; power loss was minimum, the trip north cost us around $600 on gas driving all over the place, so great in that sense. The red engine light has been on since the gas conversion, due to apparent conflicting between the gas computer and the Holden one. The transmission jerks, the car stalls/powers out randomly, slow reverse engagement. The latest is it struggles to start on petrol; you basically have to start it on gas first, even after the fuel pump was changed... It's pretty much cactus and I'm not wasting any more time with it. I think they were built as the cheapest entry level SUV 4x4 at the time, like buying cheap Chinese items that last a few years, but look good.
Future plans... start a savings account for new Hilux, 3rd party insurance on the Frontera now for sure, maybe purchase another wreck and swap parts, but as it's RW and is clean and still drives, run it into the ground until buying a Hilux... The funny thing is I'm probably spending an equivalent on the vehicle including bits and pieces to what it would have cost me if I had left it on petrol, if not more...