Unaslob
I found this cigarette lighter outlet powered 200 watt instant defroster on the internet.
http://www.vectormfg.com/site2/vecto...roducts_id=118
The link is to the manufacturer -- -- I don't know if they sell direct. I saw it elsewhere on the internet for $25 or more. If you decide to try it, let us know how it works.
Another possibility would be a short section of 12 volt electrical heating tape. I know it exists, but I don't know where to get it.
Good luck,
George