I bought two new dew heaters. They are sold to be used on camera lenses and powered from USB. I have modified them to reduce the power from 8 Watt to 2 Watt which will be enough for my demand.
Some photos and documentation from this project:
http://www.astrofriend.eu/astronomy/...ting-band.html
This will be battery operated and I try to reduce the power consumtion of the equipment.
/Lars