When I built city buses, the air brake system was a nest of Eaton "Synflex" tubing; hard yet flexible thermoplastic (Polyester? Polyamide?) with fiber reinforcement. I expect semi-trucks or anything else with air brakes is built about the same. A person could go to a semi-truck repair shop, and maybe buy their cutoff scraps and get long enough sections to fab a GMT400 fuel system. Brochure claims it's resistant to gasoline, but I've never dropped a sample into a jar filled with gas. Worst part would be coming up with the fittings to connect it to the rest of the vehicle. What we used on the buses was ordinary-looking brass compression fittings, but with metal sleeves to support the ID of the hose where the brass ferrule clamps it. MAYBE those brass compression fittings were somehow "Synflex specific", I wasn't the buyer of them, I don't know where they were sourced. Maybe get the fittings from the same truck shop you get the Synflex from.
_ga=2.11790387.664555211.1684016661-1517327216.1684016661[/URL]