I had one of Peter Fogwills trailers to start with which was very open to the elements.
Sadly one of the disadvantages of using a trailer is freezing weather. Although we could disconnect the pump and blow the water out of the delivery hose, the hose that supplies the pump always froze solid. Even pouring kettles of boiling water over it was a waste of time.
This is one of the reasons why we now have a van mount each, with an old modified 750w wall heater thermostatically controlled to keep the vans frost free in weather such as we are experiencing now.
Spruce