Designing Kitchens and Bathrooms - bath fan leak

I installed a bath fan/light/heater unit in my bathroom this summer and everything worked just fine. Now on three different occassions in the last couple months, I've had water leaking from the units faceplate. When I opened up the unit, there is a small pool of water where the exhaust exits the unit to the plastic tubing going to the roof vent. I don't believe the water is coming in from the roof cap since the ceiling itself is not getting wet. It is just contained in the fan unit. Since I live in the Midwest, could the cold air in the attic be causing enough condensation in the vent hose causing it to pool up in the fan unit? If so, is there a better venting hose that can be used other than the thin plastic one supplied with the fan unit? Any other ideas of what is going on would also be helpful. I have made sure there is no snow blocking the roof cap, so that shouldn't be causing the problem.

Sounds like you diagnosed your own problem.
The cold air in the attic is causing the warm, moist air from the bath exhaust fan to condense in the vent hose.
Need to wrap it with some insulation in the attic.
Good Luck!