When in doubt, use titanium.
Brad Bedell's Supercharged V6 Toyota MR2 that won SportCompactCar's USSC used titanium tubing for the coolant lines in the tunnel. Awesome or what?
examples
Mech, Were you working on a side-by-side or one of those Honda powered buggies? What's your opinion on the importance of weight reduction compared to aero drag reduction for cars on this forum?