The problem with the GoPro is it fogs up, very easily.
That is so true, especially up here in Qld.
I never have that issue on my ride home from work (I use mine every day on my commute) because the camera is sealed in an air conditioned environment.
When I leave from home is when I get the fogging and it is morning/cooler outside, so I usually put the case under the air con or in the fridge and then seal it. This seems to work most of the time.
I now also carry both the open and the sealed backs and only ever use the sealed back when it is seriously raining, allowing a llitle ventialtion to limit the fogging.