Agreed. Water cooling will move the heat from the DIN enclosure where space is tight, out to a space that is very likely to have cooler air. You still have to radiate the heat but the likelihood that the ambient air in the car is above 110 for extended periods while the PC is on is pretty low.
And yes, I'm aware that the temps in the car can reach 150 or more when closed up but those temps will fall very quickly with the windows open or air conditioner on.
In any case, I don't think Sonic is considering water cooling right now. It's about whether his system sucks or blows.
Back on topic!