Indeed!
Copper would need to be well supported. Any movement will cause it to work harden and eventually crack. If you want something that is light weight and a little easier to bend than stainless, go with 5052 in -O- condition (dead soft). It is easy to work with, once you understand bend allowance. Aluminum line still needs to be supported to prevent cracking. In my opinion, hard-lines are not self-supporting and should not be used to support anything, including Y and T fittings. You will also need to have a flex line between any component that will move during flex and vibration i.e. engine/hull, fuel filter, pump, etc. as well as support at the end of the hard line. Aluminum and copper tubing will require double-flares unless you go with a Swagelok style compression fitting.
Although I don’t consider stainless line to be self-supporting, it is some amazingly tough stuff and I have seen some plumbing practices that fatigue and crack other materials. I will probably run 304 SS on mine for cost and ease (relative) of forming. If max corrosion resistance is your thing, 316 SS is the alloy of choice, but it is harder to bend and work hardens while cutting/flaring. If you go the 316 SS route, you will be much happier with Swagelok fittings (except for the price) over AN/JIC fittings.
