Just let you all know, while I was stuck out here in the winter, I bought a heated waistcoat (Keis) from Hein Gericke for £89.00. It has to be one of the best investments I have ever made. I got the heated boot insoles too.
I decided to look into making heated clothing, and its really simple. I have attached a couple of pics. You use Teflon coated wire, the theory behind it is 33 feet of wire, attached to a 12V battery, usually at 4 amps will produce around 55 watts of heat. My home made jacket is as good as the Keis waistcoat. You can make up on off switches etc, I have a control unit that I got with the waistcoat, I purchased the connectors from Maplins.
I bought the heated kit from the internet £25.00 that includes all the Teflon wire, waterproof connectors with inline fuses, eventhe needle, not sure if I am allowed to advertise it, so PM me if you are interested in the details.
I rode the bike until I started to get cold, switched on the jacket, and it was the best feeling ever, as the warmth kicked in.
Hope you find this helpful, sorry its late on in the winter, but we do get cold spring and summer days.
Next I will be looking into a coffee and tea maker for bikes (Only teasing)