The units mounted orientation for my installation will be "backwards" with the rear of the fan facing forward. And yes, installing it the "correct" way would make a wonderful funnel for any rain!
Since it folds down nearly flat, and does not
have the traditional MaxxAir big box scoop, I think it will do fine when in the "closed" mode while towing.
I don't believe there is a "lock" feature of the unit per se. Powering off the unit, or using the Open / Close button, brings the lid down in to the Closed mode. That should suffice as there should not be a lot of wind on the trailers top with it behind my Expedition.
I just received an email from my dealer that the fan should be in late this week.