My 2002 Boxter has the odor of coolant after shutdown. Am not seeing any on the floor. Not in the rear trunk and mat is not wet there. Maybe a radiator cap?
You probably have a leak on the front of the engine that is dripping on the cover and never reaching the ground. Try sticking your fingers on top of the cover, just about the center of the engine and see if you can feel any crusty stuff up there from evaporated coolant (or drop the cover and see if it's covered with dried stuff)...
You posted a link as if you replying to this thread.....
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-99' Zenith Blue 5-spd...didn't agree with a center divider on the freeway
-01' S Orient Red Metallic 6-spd...money pit...sold to buy a house
It's also important to note that you won't see a wet spot in the carpet per-se. The rear carpet sits up on a platform of sorts, and the coolant typically drips underneath that.