Hi, looking for some advice please

I have a heavily pregnant mare who will shortly start suffering with the
heat and flies, so I wanted to put a ceiling fan in the field shelter for
her to keep her cool and keep the flies away. I'm thinking of a cheapie
ceiling fan something like this:
http://www.argos.co.uk/static/Produc...er/4306793.htm

The field shelter is of a wooden construction with a metal sheeting roof.
It has two large openings either side, and the fan will be situated approx
4' inside the building away from the doorway. I was planning on mounting
the fan to a plinth, which I would then mount between the purlins on the
roof.

Is this doable? Am I running a big risk with condensation and damp fog?
I'm not sure what IP rating I would need really - IP44? And do fans that
comply with this exist? The power supply is RCD protected. Is there any
way of making this workable? I also have a 12v supply if this would be
better - would I be better using a car-radiator type fan? Would this
actually do anything though if the ceiling of the field shelter is approx
11' high?

Many thanks.