(for my own curiosity) Why would you like to transport the boat in a
closed trailer?

The reason is that I can use it as storage when I park it next to my house
or on other places.
So, the transport is not the reason to close it, but the parking.

When it is closed, it is protected against wheater (winter) and against bad
people.

I have no good storage location next to my house, beside parking-places for
cars.

Frans

(So, it isn't a problem to drive with an open one, but I want to park it
closed/protected in the city)