Hye trent
Im a LPG gas fitter and believe me, a lot of the Gas systems that we do at my work are laptop programmable standalone LPG vapour systems which work very VERy well.. there is still a large proportion of old school falcon and commo set ups tho
drop tanks and the like are pretty common these days too, however there is many strict guildlines in which the installation has to abide by. tank has to be so and so mm off the ground, theres "escape" angle, certain mm away from the exhaust system, mounting hardware, etc etc.
with a 2004 onwards pajero the rear cargo area has a storage area, this is removed and the floor is cut out of the car, a bracketed tank and new lower floor are fitted pretty much replacing the rear of the car. the result is a tank you cannot see and doesnt take any extra space up.
not all cars are like this tho... some are real pricks to get tanks into and keep it legal.