If you do not have some sort of eyepiece heater, a great way to avoid frost is one of those disposable hand warmers. You activate it, and rubber band it to the eyepiece. It works like a charm. As Don says, pit n pole is especially prone to frost, but one handwarmer will keep your eyepieces clear for about 6 or 7 hours. Depending on the scope design, sometimes it can just be mounted on the eyepiece holder or the focuser, otherwise you need to switch it with the eyepieces. Quoting "Don J. Colton" <djcolton@piol.com>:
I haven't been to Pit-N-Pole for several years but since it is near the local valley floor it is particularly susceptible to frost and dew. I was out observing in Sandy and no frost appeared all night long but the skies were light polluted. The weather forecast said the dew point was 13 deg. F. I suspect the dew point was much higher at Pit-N-Pole or did it get that cold.