Interesting, I just ran into this exact problem!
I ended up researching, and found that PVC has an excellent compatability with natural gas. I ended up using 3/4" id, but I may have been able to get away with something a little smaller, but 3/4 worked, so I didn't want to chance anything else.
McMaster Carr offers PVC hose, and that is what I have used and it works perfectly. If you watch my youtube video, about half way through, I show you the hose, here is the link:
I found some really nice natural gas quick disconnects on Ebay and used those also.
This is not "approved for natural gas" hose, but if you read on the internet, modern gas mains that are buried under ground are made of PVC, and residential natural gas is very low pressure, .5 psi, so hose strength is not the issue, it is chemical compatability, which PVC is excellent for.
But, do you own research, this may not be the best for your setup, but it works great for me. My hose is 25' long, but you can get it in about any length/diameter/color you want.
Hope this helps!!!