Paul apparently 3-5W of power is sufficient to keep the dew off an SCT corrector plate and on the site that I have quoted the author used a resistance of 14 ohms to give about 10 watts (at 12V) maximum heating. BTW, you can't solder nichrome wire. As I said the design is as simple as it gets (cheap too, bits would be under $10) and because it's switchmode it is also efficient power wise...
Go on have a go, short of sticking your tongue on the battery there's no way you'll hurt yourself....
