Hi Ing,
I read that and concluded that you are not experiencing the UK weather at the moment!
I look forward to coming to Melbourne for some warmth at New Year!
There is already a breather hole under the toe strap. However, if it is hugely warm in AUS that is not a bad idea in order to get some extra ventilation. Don't forget to put it back in though!
I don't bother ever taking mine out in the UK. This past week the air has been moister on the outside!