If this is for astrophotography, it helps if you select a site that is NOT PRONE to having dew form:
Selecting a site for astronomy purposes
The dark site I frequent, dew has never been a problem. There have been many nights that our location was crystal clear and dry, but driving down into Katoomba the place was fog bound and sopping wet from dew. Would never have guessed this was the case at the obs site
For your immediate problem and for other occasions, I too second the suggestion of making your own dew shield. Made out of foam rubber tends to insulate a bit better too.
Alex.