I can vouch for all Lizzie's points. We had Gaslow on our last van, but so far haven't been able to afford the installation on our present one, as we're now in France where they want 800€ for it!
But we had the last van for 9 years, and visited lots of different countries. There were some which only had occasional garages selling LPG, but I never found it unobtainable.
One other advantage - if you wait until a "normal" bottle runs out, it's obviously always while you're using it. If you change before that, you waste some gas. But you can top up a refillable anytime, none is ever wasted. So if you're going to a country where it's a bit rarer, you top up whenever you see it.