Any tubing will stand up. The pressure in less than 60 psi and the temp is probably not over 200 deg. Copper will work but must be supported well with clamps because it tends to work harden and crack if allowed to vibrate too much. Steel or stainless steel will do also. The stainless is slightly more expensive and unless you go to a specialty shop you might have to buy a 20 ft. length. Stainless fittings are also a bit pricey.