I installed my T3 last week, and after install, even with the front bulkhead seal in place, you can see daylight on both sides where the bed rails are higher than the bulkhead rail.
Still, after a gully washer last night, there didn't seem to be much, if any, water in the bed. Granted, I wasn't driving it - the truck was parked all night - but still, that's impressive.
This is a nice-looking tonneau cover that truly is easy to install/remove.
I plan to remove it for snow storms >6", to prevent too much weight from sitting on it. That, or fold it into the open position and click the safety straps in place. What are other people doing?
-John