A number of years ago the regulation of propane tank pressure did change for safety reasons. It used to be that one regulator was used at the tank.Later a higher pressure regulator was used at the tank and a lower working pressure regulator was used just outside of the house/building, etc. On very rare occasions a tank regulator would have its vent ice over and wind up delivering high pressure to the house. I have known of two instances where such pressure produced flames to the ceiling. Luckily in both instances people were at hand to promptly shut off the flow and thus stopping a house fire. Two regulators practically elimiminates this chance of fire. I agree that 100 pound bottles would probably be your best option. Farm supply stores often sell them new. Some dealers correctly refuse to fill older bottles owned by another dealer or without an updated inspection. I would also suggest that you speak to the dealer you will have fill such bottles and ask about getting an automatic switch over valve to supply the regulator. When one bottle runs out the device will automatically switch over to the full bottle. The empty bottle can even be removed for refilling without disrupting the flow. Campers typically have such a set up. Another thing---I don't believe that low pressure regulators are set at .5 lbs. pressure. I believe they are correctly set at 13 or 13.5 inches of water column pressure. Safety first as I also suggest you spring a few extra bucks for regulator covers to prevent icing.
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