I am trying to make a custom length of LP Gas supply line that has a swivel FPT fitting on each end. At first I was considering using vinyl hose, however I could not find any rated for vapor at the local hardware stores. Also, I'm not confident in adding fittings to the hose ends and preventing any gas leaks. Then I thought about flexible copper tubing. I've never used flare fittings and I know I'll have to buy a special tool for it. The thing that would actually work the best for me is rigid copper tubing where I could sweat the fittings on. Can I sweat fittings on copper tube used to supply LP gas? I have shut-off sweat-valves that are rated for LP gas, which makes me think you can. But I'm also reading sources that say I can't. I have also read sources that say I can't use a compression fitting when dealing with LP gas since it is prone to leaks.

Does anyone out there know what the right thing to do is?

A swivel joint on an LP line would be a horrible idea -- If you need flexibilty at the appliance point, then use a resin or stainless steel flexible supply after the shut-off.