In all fairness to the OP hes not saying LPG is going out of usage. he simply said to get small bottles and on board A tanks filled may be harder to find find over time if the Rv usage(demand drops in some areas of the country. Of course LPG will never vanish from the USA as its used for heating homes,trailers +commercial useage in vehicles and paving plants etc where LNG is not available.No one in their right mind price wise would use LPG for heat if there was also NAT gas at the lot line as its less than 1/2 the cost of LPG.
In Canada 1% of homes use LPG for heat.Its mostly Nat gas and some small sub sources such as wood,diesel,electric