I've looked at a propane carburetor for a chevy small block engine to be used on a rock crawler so the engine wouldn't stall during inclines but I haven't seen any recommendation on what should be used for the fuel lines from the tank to the carb. Besides rubber hoses that can break if a vehicle roles what can be used to deliver propane gas to a propane carburetor?
In Australia, our Automotive LPG hose standard is:
• AS/NZS 1869 class D
According to the following document, it appears that in the US propane hoses for automotive use needs to meet:
• NFPA 58, Liquefied Petroleum Gas Code, 11.6
• Referenced ASTM Piping and Tubing Standards
Edit: When searching for lines, make sure they meet these standards. You can get good steel braid rubber hoses all over the place.