[lutman]

Nothing wrong with copper pipes as long as the correct fittings and clamps are used.
Testament to this is how many old classic cars still run with the original brake pipes.
Main factor is dissimilar metal galvanic corrosion which comes about when using steel pipes with copper/brass fittings and vica versa.
Indeed some may argue that steel pipes are prone to rust which copper is not ?

I personally would use steel as the copper pipes could split when using booster ( servoed) systems due the higher line pressures developed.