I don't see a problem with copper
my sailboat has a fuel tank made of monel metal, which is a copper alloy, they used monel for it's superior corrosion resistance.
My boat is a '67 pearson triton 28.5 foot, and the tank is just like new inside and out.
Many fuel lines were made of copper tube in the old days.
brass and bronze are some of the best fuel line fittings you can get, and they are both copper alloys.
ken