I started running my Neu's open. I used to just put some electrical tape on the front and used Mike's rear end cover. I find running it open helps temps a bit and I haven't had any problems with dust and rocks. I know others that do the same. I just blow it out with air after a few runs.

You will be hard pressed to keep your motor temps below 150 if you are racing. 150-175 is typical and nothing to worry about for track duty. I rarely ever get above 125 bashing though.