[rick3000]

Did they test for leaks when the car was hot? I had a very elusive leak that only expanded enough to leak once the engine and coolant had warmed up for a while.

Have you noticed any condensation inside the rear trunk? Specifically, around the coolant cap?
What coolant are you using? The Porsche coolant dries as a white residue to help identify leaks, any signs of a white residue anywhere?

My first thought would be some kind of very steady and slow leak from the coolant tank or cap (Do you have the latest coolant cap?). That would explain the coolant loss and the heat. The trunk should not be getting that hot.