LPG fuel sounds more like an energy density problem than a weight of the tank problem. How much energy per pound (kilo or whatever) of LPG versus 100LL? How much energy per cubic inch (or cc) of LPG at the stored temperature and pressure compared to 100LL or Jet A?
From a weight point of view the tank would likely be heavier and there would need to be pressure regulators and dehumidification for refueling but maybe you wouldn't need a fuel pump (unless you were going to run it in Antarctica or above 20,000 feet) and not sure how you would get a sample from the sumps to see if there was water contamination. Presume LPG powered would mean fuel injected so no carb ice. Land at the nearest caravan park to refuel?