Install it in the trunk. If you get a low power cpu, like the integrated Via's, then as long as there is adequate fan cooling, summer time heat shouldnt be too big of a problem. HD would probably be the most sensitive component to keep your eye on.
As for tint, I have 5% limo in the back and I dont think it does anything to make it cooler. Also, those solar powered window vent fans are a ripoff, Im pretty sure they do next to nothing at all.