Roger
If you are going to have joints in piping the best are the metric olives - light years ahead of flared pipe. I think I've seen evry possible combination of gas plumbing over the years, "best practice" has the gas bottle outside the van with a "gas fuse" and plumbing underneath the van and entering the van beneath each appliance with an isolation tap for each appliance as well - piping is stainless steel and uses metric olives. "Worst practice" is to have everything inside the van, using copper piping laying on the floor or flopping around loose in cupboards with only the bottle tap as the cutoff.
Have a look at a few German made vans and you'll get some good ideas - many have 12V block heaters after the regulator to ensure the gas does not freeze in the piping.
Have a look at a few German made vans and you'll get some good ideas - many have 12V block heaters after the regulator to ensure the gas does not freeze in the piping.