For my RC51, I use Evans Waterless Coolant. No water, no corrosion.
Never, ever have to replace coolant, except for system failure or repair.
And even then, they recommend draining the coolant into a container, then return it back to the system.
Since there's no water, no cooling system pressurization required to raise the boiling point.
IF you could possibly find one, you could use a 0 PSI radiator cap.