Hello John. 12 volt hairdryers are avail from any/most boat/caravan parts suppliers. They average $20. Any more than that, don't buy. Email John at > john_at_five-islands-marine.com.au < for good prices on them.
They do draw/use a lot of power from your battery tho. So be frugal with it's use, or buy a bigger battery.
HTH.

L.
ps. Resistor type dew heaters are easily made. Lots of diff designs around.