Hi,
good idea, but to be useful you,ll need some meaty cables,here,s a indication of power needed for 12v imersions, A 12 Volt 100 watt immersion will heat 1 Litre of water 1 degree C in 1 minute and draws just over 8 Amps.
A 12 Volt 400 watt immersion will heat 1 Litre of water 4 degrees C in 1 minute and draws approx 35 Amps.
A 12 Volt 600 watt immersion will heat 1 Litre of water 6 degrees C in 1 minute and draws around 50 Amps
http://cgi.ebay.co.uk/12v-Volt-1%22-WAT ... 06fe2eabb7
regards Trev