If the copper pipes (is approved for brakes) are firmly fixed, they can not move and break. We have big problems with rust here in Denmark and copper pipes do not rust easily. The car has been approved by an engineer, where he has made a pressure test of the brake system. and vehicle inspection, also make a test before it may even run on public roads.
Stainless steel pipes are very nice and super strong. are maybe a little overkill for me