Guys, thanks for all the suggestions. Yea, I thought that a couple of NACA ducts on the sides might be the next step if required. However, as Andy points out, I also have the feeling that the two existing holes might be sufficient given the model will be sucking in air at considerable speed. It also expands into a large chamber which should help to setup a pressure gradient. It could be that the battery and ESC will actually be receiving an expanding jet of air right on to them. The main concern, if any, is actually the motor - I'm quite certain that the battery and ESC will remain cool as they are both running at low currents for their rating. Actually I was wondering not so much whether this would be adequate cooling but rather whether they would produce significant noise in flight!

David.