copper is a good heat exchanger, but it can have a tendency to work harden from vibration and become brittle. not saying how long this could take, but something to take into consideration. some places ban copper fuel line for just that reason, but i have seen many, many vehicles of all descriptions using copper for all kinds of fluid line applications. i guess it is up to the individual to use copper or not. if you decide to do so, i guess a good inspection schedule would catch any problems that could possibly occur.