I was considering the black rubber propane lines for the hook-up to the appliance from the black pipe since they wouldn't be as vibration damage prone. The stainless steel flex I have seen (Home Depot) doesn't recommend RV installation, I assume it's a vibration issue. Whatever I use from the pipe to the appliance won't be passing though anything but air and will be under 12" long. I guess burning though will have to be weighed against cracking
I've also thought about just using good ol' copper to do the hook up off the black pipe trunk, that's how the gas was run in the 07' fith-wheel I looted for parts.