It might be worth checking that your aircon is draining properly too, as that can cause the same symptoms when the drain is blocked or damaged. You may not be using an aircon setting, but the aircon is switched on when you select one of the demist settings - so it will still de-humidify the air, and chuck it out of the bottom.
The drain pipe comes out of the chassis member, directly under the passenger footwell. I suggest that you go for a run with the aircon on, and then park up somewhere that's dry. If you don't have a puddle forming underneath the passenger footwell, then that may be your problem.
